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Hair Challenges and Treatments Around the World

Experts from different continents sharewhat is trending in their regions.
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Around the world, hair loss is no longer being treated as an inevitability, despite factors such as GLP-1 receptor agonists increasing its incidence. From pharmaceuticals to regenerative therapeutics to device treatments, dermatologists’ treatment armamentarium continues to expand. Practical Dermatology asked experts from around the world to weigh in on what is exciting them most about current and future hair treatments.

AUSTRALIA

Rodney Sinclair, MBBS, MD, FACD

Director, Sinclair Dermatology

Professorial Fellow, Department of Medicine, University of Melbourne 
(Melbourne, Australia)

In Melbourne, it is very common for women to experience increased hair shedding that may last a few weeks or even a few months. The trigger may be recent surgery, a high fever, or especially with the rising popularity of GLP-1 receptor agonists in Australia, recent weight loss. Sometimes, it is impossible to pinpoint the trigger.

However, recurring episodes of increased hair loss, known as telogen effluvium, have recently been shown to be a trigger for female pattern hair loss. Caused by hair follicle miniaturization, female pattern hair loss under the microscope looks identical to male androgenetic alopecia. The hallmarks of female pattern hair loss are progressive widening of the central part line, loss of volume in the ponytail, and eventual balding over the crown and temples.

Women experiencing increased hair loss may benefit from a checkup with their dermatologist, as early treatment can prevent future balding.

USA: WEST COAST

Nada Elbuluk, MD, MSc

Assistant Professor, Department of Dermatology, Keck School of Medicine 
of USC

This is an exciting time for the field of alopecia as there are treatment advances happening for multiple types, particularly nonscarring alopecia. I am excited about a few emerging treatments for androgenetic alopecia and advanced technologies for monitoring of alopecia.

Topical clascoterone is a novel androgen receptor inhibitor that blocks DHT directly at the hair follicle. Its phase 3 SCALP 1 and SCALP 2 trials showed a relative improvement in target-area hair count versus placebo and a safety profile comparable to vehicle.1 If approved, this could offer a novel topical treatment option for androgenetic alopecia.

Additionally, a new regenerative treatment known as PP405 targets hair follicle stem cells. In its phase 2a trial, the drug was well tolerated with no systemic absorption and compared to placebo showed improvement in hair density in a subset of men with more advanced hair loss by as early as 8 weeks.2 It also induced new growth from follicles where no hair was previously present. This is promising for patients who previously have not responded to existing treatment options.

Currently, methods for monitoring hair-loss improvement for those under treatment vary and can range from subjective clinical exams to use of photography to trichoscopic imaging. Incorporation of artificial intelligence in the trichoscopic imaging can provide standardized, quantitative data that includes measuring hair density, shaft thickness, and follicular structure. This can provide a much more objective and precise way to monitor whether a treatment is actually working and to what degree it is working compared to visual assessment alone.

Together, these advances point toward a future of more effective, mechanism-targeted treatments paired with the precision tools to better evaluate their efficacy. I am hopeful in the coming years we will also start to see clinical trials for treatments for scarring alopecias.

USA: EAST COAST

Antonella Tosti, MD

Fredric Brandt Endowed Professor of Dermatology and Cutaneous Surgery, University of Miami

In Miami, the two hair disorders I see most frequently are telogen effluvium and female pattern hair loss (FPHL). Women are disproportionately represented in my practice, perhaps because men are more likely to seek a quick solution and may mistakenly view hair transplantation as a replacement for medical treatment rather than one component of a long-term strategy.

Miami’s heat and humidity create hair challenges. To control frizz, many women have keratin treatments. These procedures may cause scalp irritation, followed by increased shedding that can unmask previously subtle FPHL. Chronic sun exposure is another frequently overlooked problem. Many women protect their facial skin but leave the scalp uncovered, especially along an increasingly wide central part. Ultraviolet (UV) exposure causes oxidative stress and scalp inflammation and worsens FPHL.

Heat, sweating, and frequent use of heavy styling products exacerbate seborrheic dermatitis, which is extremely common in my patients. Finally, Miami’s highly diverse population means that I frequently see traction alopecia and central centrifugal cicatricial alopecia in patients of African descent. Recognizing these conditions early is essential because continued traction or untreated inflammation will eventually produce irreversible hair loss.

EUROPE

Lidia Rudnicka, MD, PhD

Head of the Department of Dermatology, Medical University of Warsaw (Warsaw, Poland)

In Poland, a distinctive aspect of hair and scalp care is the strong academic tradition in trichoscopy. Polish dermatologists have been among the leading contributors to trichoscopic research and education, making scalp imaging an integral part of the diagnostic process for conditions such as androgenetic alopecia, alopecia areata, and scarring alopecias. The Polish hair team is now also helping to shape the path toward the routine use of line-field confocal optical coherence tomography (LCOCT) in clinical practice, further refining noninvasive diagnosis of hair and scalp disorders. Another important feature of Polish practice is the systematic focus on hair loss caused by autoimmune diseases and characteristic comorbidity patterns. In patients with alopecia areata or chronic telogen effluvium, clinicians routinely consider and screen for associated autoimmune diseases, such as systemic lupus erythematosus, thyroid disease, Satoyoshi syndrome, and other immune-mediated conditions, integrating scalp findings into a broader immunological context. At the same time, the availability and reimbursement of modern systemic therapies, including biologics and JAK inhibitors, allow earlier intervention in autoimmune disease and reduction of hair loss linked to autoimmune phenomena. Access to these novel drugs creates the Polish landscape of hair and scalp disease management, but a key challenge remains patient education so that patients recognize dermatologists as the primary experts in hair loss management.

SOUTH AMERICA

Mariana Andrade Lima, MD

Recife’s Holy House Hospital 
(Recife, Brazil)

There is something quietly subversive about treating hair loss with a tattoo machine. Microinfusion of medications into the skin (MMP®), described by Arbache and Godoy in 2013, delivers small, uniform drug volumes into the superficial dermis while the needle stimulates the follicle, as with microneedling.1 Two mechanisms, one pass, which I find genuinely appealing. The field still needs to consolidate its controlled data,2 but the early clinical signals are encouraging.

In androgenetic alopecia (AGA), the efficacy signal is tangible. Uncontrolled series report real regrowth: three monthly sessions of minoxidil–dutasteride tattooing dropped the median top-quadrant Severity of Alopecia Tool (SALT) score from 60% to 40% in 15 men;3 five sessions with copper peptides and deeper needling pushed median top-scalp-area regrowth to 26.5%;4 and the largest dataset, 30 men on dutasteride monotherapy followed for 12 months, found stabilization or improvement in almost all.5

The question that has shadowed the technique since Contin’s first AGA report in 2016 is whether the drug or the needle does the work.6 Our placebo-controlled pilot put it to the test: eight men, dutasteride versus saline microinfusion, no substantial difference between arms—because needling with saline improved AGA as well.7 Underpowered, yes, but it remains a thought-provoking result in the field, and it echoes Contin a decade on. The one controlled design that favored the drug is a split-scalp methotrexate trial in frontal fibrosing alopecia, where treated halves improved while untreated halves progressed8— a reminder that the answer may differ by disease and by drug, and that targeted drug delivery can make a measurable difference. Alopecia areata with triamcinolone and chronic telogen effluvium with minoxidil remain at the case-report level,9,10 keeping the door open for future exploration.

The safety picture deserves the same balanced attention. The local-action rationale of “drug where you want it, little elsewhere” is plausible but still being built. A placebo-controlled trial of minoxidil microinfusion lowered diastolic blood pressure significantly, which the authors interpreted as evidence of systemic absorption;11 a single methotrexate session transiently raised transaminases in a patient with prior hepatotoxicity from oral methotrexate.12 Both findings are minor and reversible, but together they make systemic absorption something to consider, especially for hypotensive or hepatotoxic agents. On the whole, tolerability is a strength: brief desquamation, manageable pain, and no hair-shaft breakage make the procedure acceptable in practice.

I remain curious and optimistic, though I prefer to keep my feet on the ground. MMP is a clever, well-tolerated platform with a believable signal in AGA and a promising one in other conditions. The evidence is still built on small series, mixed protocols (such as 1.0–2.0 mm, 70–120 Hz, or assorted drug blends), and photograph-based endpoints that highlight good responders, but it consistently points toward benefit. The open question is no longer whether patients improve but exactly what drives that improvement and how to quantify the systemic exposure with precision. Until then, I use MMP with genuine confidence in its clinical utility, while remaining keenly interested in the data that will tell us exactly how it works and how safely we can push it.

ASIA

Abdullah Alkhalifah, MD

Director, Department of Dermatology, 
Prince Sultan Military Medical City
(Riyadh, Saudi Arabia)

Topically applied minoxidil has served as the mainstay of pharmacotherapy for androgenetic alopecia since the 1980s, frequently augmented by platelet-rich plasma (PRP) therapy. Recently, low-dose oral minoxidil has largely superseded topical regimens.

In the Middle East, patient expectations often necessitate the integration of regenerative procedures alongside conventional pharmacotherapy, as monotherapy is frequently perceived as inadequate. Autologous cellular micrografting addresses hair follicle miniaturization by delivering tissue-derived progenitor cells and growth factors harvested from the androgen-resistant occipital scalp. Isolation protocols vary and may incorporate photobiomodulation of cell suspensions.

Another trending procedure, autologous stromal vascular fraction (SVF) therapy is gaining clinical traction. Stem cells are isolated through centrifugation of lipoaspirate harvested from abdominal fat.

Although both autologous modalities exhibit favorable safety profiles as single-session interventions, further standardization of isolation kits and processing parameters is required to optimize therapeutic efficacy.

Wenyu Wu, MD, PhD

Director, Department of Dermatology, Huashan Hospital, Fudan University (Shanghai, China)

China's hair science and hair-loss field is advancing rapidly. Real-world research on JAK inhibitors is expanding, while robotic hair transplantation and AI are bringing greater precision to diagnosis, treatment, and research. Innovative Chinese-developed therapies (including Hengrui’s ivarmacitinib, Kintor's GT20029, and Hope Medicine's HMI-115) reflect an increasingly dynamic ecosystem connecting clinicians, scientists, engineers, and industry. Together, these developments are helping translate new discoveries into meaningful hope for people with hair loss worldwide.

AFRICA

Ncoza Dlova, MBChB, FCDerm, PhD

Head of Dermatology, College of Health Sciences, School of Clinical Medicine, University of Kwazulu-Natal
(Berea, Durban, South Africa)

In South Africa, hair is deeply intertwined with culture, identity, and self-expression, but some common hair-care practices unfortunately can contribute to preventable hair loss. Tight braids, weaves, and extensions, particularly when applied to chemically relaxed hair, can cause and aggravate traction alopecia, which may become permanent if not recognized early. Hair care should, therefore, focus not only on appearance but also on preserving the health of the scalp and hair follicle: hairstyles should not hurt, pull, or cause persistent scalp tenderness.

Infrequent hair washing sometimes may be influenced by cultural and practical considerations, including the maintenance of some of the aforementioned styles. The term "protective hairstyle" can be misleading; in addition to some of these styles potentially increasing the risk of hair breakage and traction alopecia, they can encourage infrequent hair washing and accumulation of residue on the scalp, resulting in seborrhoeic dermatitis and other scalp pathology.

Prolonged intervals between washes may allow the accumulation of scalp scale, sweat, and hair-product residue, which can contribute to scalp discomfort and certain scalp disorders. Where practical, we encourage regular scalp and hair cleansing, ideally about once per week, using gentle products including hair conditioners that help soften the hair and make it more manageable for grooming.

For young girls, we encourage natural, simple, and manageable hairstyles, including shorter styles where appropriate, that minimize pulling and manipulation of the hair. Promoting healthy hair-care habits from an early age can help protect the hair follicles and prevent potentially permanent hair loss at an early age.

SOUTH AMERICA

Brazilian Keratin Treatments and Acid Hair Straighteners: Hair-Fiber Effects and Emerging Health Concerns

Bruna Duque Estrada, MD

Professor, Hair Studies Center, Santa Casa da Misericórdia do Rio de Janeiro
(Rio de Janeiro, Brazil)

Brazilian keratin treatments (BKTs), also referred to as Brazilian blowouts or progressive straightening treatments, differ from conventional hydroxide- and thioglycolate-based relaxers in both their chemistry and mode of application. These procedures typically combine the application of a straightening formulation with blow-drying and repeated passes of a flat iron, frequently at temperatures of approximately 180–230°C. Early formulations commonly contained formaldehyde or formaldehyde-releasing compounds, whereas newer products may contain glyoxylic acid or related derivatives. Importantly, heat is not merely used to finalize the hairstyle but is an integral component of the straightening process, promoting dehydration and chemical and conformational changes within keratin.1 The magnitude and persistence of straightening are influenced by thermal exposure, including flat-iron temperature and repeated passes over each hair section.

Unlike conventional chemical relaxers, BKTs are frequently perceived as conditioning or restorative treatments because they produce an immediate improvement in fiber alignment, smoothness, shine, and frizz control. However, these cosmetic effects should not be equated with structural repair of the hair shaft.

From Formaldehyde to Acid Straighteners

Recognition of formaldehyde toxicity and subsequent regulatory restrictions stimulated the development of products marketed as “formaldehyde-free.” These formulations may contain glyoxylic acid or glyoxylic acid derivatives, including glyoxyloyl carbocysteine and glyoxyloyl keratin amino acids. A formaldehyde-free label, however, should not be interpreted as synonymous with risk-free. Product labeling may not fully reflect the compounds generated during heating, and exposure to potentially harmful vapors remains a concern during high-temperature procedures.2,3

Glyoxylic acid-based straighteners have become particularly widespread as alternatives to formaldehyde-containing formulations. Unlike conventional alkaline relaxers and thioglycolates, their straightening effect does not primarily rely on the cleavage and rearrangement of disulfide bonds. Spectroscopic studies suggest that glyoxylic acid, combined with dehydration and heat, induces chemical and conformational modifications in keratin that contribute to maintaining the hair in a straighter configuration.1

Immediate Smoothness and Delayed Hair-Shaft Damage

One of the most intriguing characteristics of acid straightening is the discrepancy between its immediate cosmetic result and its effects on fiber integrity. Immediately after treatment, hair may appear exceptionally smooth, glossy, aligned, and resistant to humidity despite having undergone substantial chemical and thermal stress. This apparent paradox reflects two distinct but partially overlapping processes: heat-dependent chemical and conformational reshaping of the fiber and transient surface conditioning.

Microscopic studies have demonstrated coating-like deposits around the hair fiber after some acid-straightening procedures. Such deposition may temporarily reduce the visual and tactile expression of cuticular irregularities and enhance light reflection.4-6 However, the precise chemical composition, organization, and persistence of these deposits have not been fully established.

For glyoxylic acid, model-compound experiments and Raman and infrared spectroscopic analyses support a reaction between its electrophilic carbonyl group and nucleophilic amino groups in keratin, including lysine residues, with the formation of imine bonds. Dehydration and heat are central to this reaction and are accompanied by redistribution of keratin secondary structure and conformational changes in disulfide bridges. Microscopic and spectroscopic findings therefore suggest that the more persistent straightening effect depends primarily on chemical and conformational rearrangements within the fiber rather than on the formation of an external polymer layer alone.1

The immediate smooth and glossy finish may be further enhanced by the formulation vehicle and conditioning co-ingredients. Depending on product composition, silicones, cationic polymers, hydrolyzed proteins, and other film-forming agents may adsorb to or deposit on the cuticular surface, reducing interfiber friction and static flyaway, smoothing raised cuticle scales, and improving hydrophobicity and shine.7 By promoting a smoother cuticular surface and more uniform fiber alignment, these deposits can increase light reflectance and perceived luster.7 Because straightening formulations are multicomponent systems that vary substantially among products, the observed layer is more accurately described as a formulation-dependent cosmetic surface film or surface coating rather than as a uniform biofilm intrinsic to all acid straighteners. Such deposition may improve the optical and tactile appearance of the hair without constituting structural repair of cuticular or cortical damage.

Brazilian academic studies provide direct morphological evidence of coating-like surface deposition following some acid-straightening procedures. In a doctoral study from the University of São Paulo, scanning electron microscopy demonstrated an “enveloping” coating after the application of multicomponent formulations containing glyoxylic acid or formaldehyde, with the coating being more evident with the glyoxylic acid-containing formulation.5 A subsequent study from the same institution evaluated a formulation containing glyoxyloyl carbocysteine and glyoxyloyl keratin amino acids at pH 1.0 and 2.0. The lower-pH formulation produced greater straightening and cuticular alignment, together with more pronounced changes in tensile strength, tryptophan content, and keratin structure. Scanning electron microscopy also suggested film formation around the fiber, with partial removal after five standardized washes.6 These findings support formulation-dependent surface deposition but do not demonstrate that all acid straighteners produce a chemically uniform polymer film.

Beneath this cosmetic effect, significant structural injury may occur. An experimental comparison of glyoxylic acid with sodium hydroxide, guanidine hydroxide, and ammonium thioglycolate demonstrated greater protein loss with glyoxylic acid—approximately 3.5 μg/g, compared with approximately 2.5 μg/g for conventional straighteners and 1.12 μg/g for untreated hair—indicating damage involving both the cuticle and cortex.4 In this experimental protocol, a commercial glyoxylic acid-containing formulation was combined with blow-drying and five flat-iron passes at 200°C.4 Spectroscopic evidence further indicates that heat activation is accompanied by conformational changes in keratin, including alterations in α-helical structure and disulfide-bond conformation.1

Pre-existing bleaching may increase the susceptibility of the hair fiber to acid straightening. In an experimental study, hair bleached before acid straightening exhibited more pronounced microstructural damage and an approximately threefold increase in total porosity compared with virgin hair subjected to the same straightening procedure.8 However, available comparative studies have been based on controlled single-treatment protocols. These findings should therefore not be directly extrapolated to repeated applications, overlapping treatment of previously acid-straightened areas, or hair affected by long-term environmental weathering, for which direct comparative evidence remains limited.

Clinically, these structural changes may manifest as increased dryness and surface roughness, loss of luster and flexibility, increased frizz, and greater susceptibility to breakage.4,8 Excessive thermal exposure may also produce bubble hair, an acquired hair-shaft abnormality characterized by heat-induced, gas-filled cavities within the hair shaft that can be detected by trichoscopy or light microscopy.9

Deterioration in hair quality after acid straightening is likely multifactorial. As the initial smoothing effect gradually diminishes, pre-existing or initially less apparent damage may become more noticeable, while the procedure itself can generate new structural injury through the combined effects of the acidic formulation and intense thermal exposure.1,4 The multiple high-temperature flat-iron passes used during these procedures may therefore contribute substantially to fiber damage.1,4

Scalp Adverse Effects

The scalp is another important target of adverse effects associated with hair straightening. Highly acidic formulations, formaldehyde, formaldehyde-releasing compounds, and other ingredients may induce irritant or allergic contact dermatitis. Patients with a pre-existing impaired or inflamed scalp barrier—including those with seborrheic dermatitis, psoriasis, or atopic dermatitis—may be particularly susceptible to irritation or disease exacerbation.

An eczema-like psoriasiform scalp reaction following BKT has also been described. In a cross-sectional clinical-dermatoscopic study of 43 patients, perifollicular scaling was observed in 98%, red patches in 81%, and peripilar desquamation resembling the outer layers of an onion bulb in 74%.[10] The mean latency between BKT and onset was 12 ± 17 months, although 47% of patients developed the reaction within 30 days. Interestingly, a greater number of BKT procedures was associated with a shorter latency.10 These findings emphasize that scalp inflammation after straightening should not simply be regarded as an expected or harmless consequence of treatment.

Occupational and Formaldehyde Exposure

Formaldehyde remains an important safety concern. It is a recognized human carcinogen as well as a potent mucosal irritant and sensitizer. Hair-smoothing procedures may generate airborne formaldehyde, particularly during blow-drying and flat-ironing, potentially exposing both clients and salon professionals.2,3 

Occupational exposure is particularly relevant because hairdressers may perform multiple procedures daily over many years. Actual exposure depends on product composition, the amount applied, heating temperature, ventilation, frequency of procedures, and compounds generated during heating. Safety should therefore be evaluated according to real-world exposure rather than marketing terminology alone.

Glyoxylic Acid, Oxalate, and Acute Kidney Injury

A particularly concerning emerging complication is acute kidney injury (AKI) following hair-straightening procedures involving products reported or suspected to contain glyoxylic acid. Clinical reports and case series describe AKI developing within hours to days after exposure, frequently accompanied by nausea, vomiting, and abdominal or flank pain.11-13 A recent systematic review identified 36 AKI episodes in 34 patients, with a median onset of two days following exposure; however, the chemical composition of the product was unknown in 16 of these episodes.13

The proposed mechanism is biologically compelling. Glyoxylic acid absorbed through the skin may be metabolized to oxalate, resulting in hyperoxaluria, intratubular calcium oxalate crystal deposition, and crystalline nephropathy. In a 2024 report, a patient experienced three episodes of AKI following three separate hair-straightening procedures.11 Experimental transcutaneous exposure to glyoxylic acid subsequently resulted in increased urinary oxalate excretion and calcium oxalate nephropathy in mice.12

A 2026 exposure study provides an important counterpoint. Using dermal absorption experiments with two marketed glyoxylic acid-containing products under standardized conditions intended to approximate realistic use, investigators estimated substantially lower systemic glyoxylic acid and oxalate exposure than that theoretically associated with renal crystal formation.14 These findings suggest that exposure under the specific conditions studied may be insufficient to explain the reported AKI cases. However, differences in formulation, dose, application technique, scalp-barrier integrity, and individual susceptibility may contribute to this apparent discrepancy. Interpretation also warrants consideration of industry involvement, as several investigators were employees or consultants of manufacturers supplying glyoxylic acid-containing straighteners.14

Thus, although AKI appears uncommon, the clinical, histopathologic, and experimental evidence supports a biologically plausible association between glyoxylic acid straightening and calcium oxalate nephropathy. Nevertheless, the magnitude of risk under typical use conditions remains uncertain.

Epidemiologic Evidence Regarding Malignancy

Prospective epidemiologic studies have reported associations between frequent use of chemical straighteners or relaxers and hormone-sensitive malignancies, including uterine, breast, and ovarian cancer.15-17 These findings warrant attention but require careful interpretation.

Exposure assessment was questionnaire-based and generally encompassed heterogeneous products described broadly as straighteners, relaxers, or pressing products, without detailed information regarding their chemical composition. Consequently, the observed associations cannot be attributed specifically to BKTs, glyoxylic acid, formaldehyde, or any individual chemical. Thus, prospective epidemiologic data suggest an association, but causality has not been established, and the specific agent or agents responsible remain unknown.15-17  

An Evolving Regulatory Landscape

Regulatory oversight of hair-straightening products is evolving rapidly. In Brazil, Anvisa prohibits formaldehyde as a hair-straightening agent, whereas glyoxylic acid is not included among the active ingredients currently authorized for hair straightening and is undergoing safety reevaluation. Some previously registered glyoxylic acid-containing products may remain regularized during this process, but new registrations are not permitted.18  Brazilian regulations specify the active ingredients permitted in cosmetic products intended to straighten or wave the hair and establish their respective conditions of use.19

In the United States, the FDA specifically warns about formaldehyde released when certain hair-smoothing products are heated.20 As of August 2026, a federal ban had not been finalized, and a proposed rule that would prohibit formaldehyde and formaldehyde-releasing chemicals in heat-activated smoothing or straightening products remained pending.21 In the European Union, glyoxylic acid is currently undergoing formal SCCS safety assessment for use in hair-straightening products at concentrations up to 16%.22 These differences underscore the rapidly evolving—and still unsettled—international regulatory landscape.

Clinical Implications and Future Directions

Despite the widespread use of hair-straightening procedures worldwide—and their particular cultural relevance and extensive use among Brazilian women—the search continues for an ideal technology that provides durable straightening and reduces hair weathering while preserving hair-fiber integrity and minimizing scalp, systemic, and occupational toxicity.

Current evidence supports a cautious and individualized approach. Only appropriately regulated products should be used, and application to an irritated, inflamed, or disrupted scalp should be avoided. Previous bleaching, coloring, chemical straightening, and substantial thermal damage should be specifically assessed, as previously weathered fibers are likely to be more vulnerable to additional injury. Thermal exposure should be minimized whenever heat-activated straightening is performed. As a practical harm-reduction strategy, the authors favor minimizing repeated flat-iron passes rather than pursuing a more rigid or persistent straightening effect through repeated high-temperature passes. This represents a pragmatic harm-minimization recommendation rather than an experimentally established safety threshold.

Brazilian keratin treatments and acid straighteners should therefore not be regarded as inherently restorative or necessarily safer alternatives to conventional relaxers. “Keratin,” “formaldehyde-free,” and the immediate appearance of smooth, glossy hair are not synonymous with structural repair or safety. Further research is needed to develop straightening technologies capable of achieving satisfactory and durable cosmetic results while minimizing hair weathering, scalp inflammation, occupational exposure, and systemic toxicity.

  1. Boga C, Taddei P, Micheletti G, Ascari F, Ballarin B, Morigi M, et al. Formaldehyde replacement with glyoxylic acid in semipermanent hair straightening: a new and multidisciplinary investigation. Int J Cosmet Sci. 2014;36(5):459-470. doi:10.1111/ics.12148.
  1. Pierce JS, Abelmann A, Spicer LJ, Adams RE, Finley BL, Gaffney SH. Characterization of formaldehyde exposure resulting from the use of four professional hair straightening products. J Occup Environ Hyg. 2011;8(11):686-699.
  2. Weathersby C, McMichael A. Brazilian keratin hair treatment: a review. J Cosmet Dermatol. 2013;12(2):144-148.
  3. Velasco MVR, de Sá-Dias TC, Dario MF, Bedin V, Fileto MB, de Oliveira AC, Pinto CASO, Baby AR. Impact of acid (“progressive brush”) and alkaline straightening on the hair fiber: differential effects on the cuticle and cortex properties. Int J Trichology. 2022;14(6):197-203.
  4. Sá Dias TC. Avaliação in vitro do efeito de diferentes processos de alisamento químico/térmico na fibra capilar [doctoral thesis]. São Paulo: Universidade de São Paulo, Faculdade de Ciências Farmacêuticas; 2015. doi:10.11606/T.9.2017.tde-07122016-111738.
  5. Goshiyama AM, Dario MF, Lima CRRC, de Araújo GLB, Baby AR, Velasco MVR. Impact of acid straightener’s pH value on hair fiber properties. J Cosmet Dermatol. 2020;19(2):508-513. doi:10.1111/jocd.13006.
  6. Gavazzoni Dias MFR. Hair cosmetics: an overview. Int J Trichology. 2015;7(1):2-15. doi:10.4103/0974-7753.153450.
  7. Lima CRRC, Lima RJS, Bandeira ACC, Couto RAA, Velasco MVR, Bordallo HN, Oliveira CLP. Alterations promoted by acid straightening and/or bleaching in hair microstructures. J Appl Crystallogr. 2023;56:1002-1014. doi:10.1107/S1600576723005599.
  8. Savitha AS, Sacchidanand S, Revathy TN. Bubble hair and other acquired hair shaft anomalies due to hot ironing on wet hair. Int J Trichology. 2011;3(2):118-120. doi:10.4103/0974-7753.90832.
  9. Sánchez-Dueñas LE, Ruiz-Dueñas A, Guevara-Gutiérrez E, Tlacuilo-Parra A. Psoriasiform skin reaction due to Brazilian keratin treatment: a clinical-dermatoscopic study of 43 patients. Int J Trichology. 2022;14:103-108.
  10. Robert T, Tang E, Kervadec J, Zaworski J, Daudon M, Letavernier E. Kidney injury and hair-straightening products containing glyoxylic acid. N Engl J Med. 2024;390(12):1147-1149. doi:10.1056/NEJMc2400528.
  11. Robert T, Tang E, Kervadec J, Desmons A, Hautem JY, Zaworski J, et al. Hair-straightening cosmetics containing glyoxylic acid induce crystalline nephropathy. Kidney Int. 2024;106(6):1117-1123.
  12. Aamir AB, Latif R, Sorath F, Chander S, Latif A, Rahaman Z, et al. Acute kidney injury induced by topical hair straightening products: a systematic review. World J Nephrol. 2025;14(4):112796.
  1. Hewitt NJ, Goebel C, Diller J, Fuchs A, Fautz R, Blömeke B, et al. Quantification of the exposure of consumers and hairdressers to formaldehyde and oxalic acid after application of hair straightening products containing glyoxylic acid. Toxicol Appl Pharmacol. 2026;515:117940. doi:10.1016/j.taap.2026.117940.
  2. Chang CJ, O’Brien KM, Keil AP, et al. Use of straighteners and other hair products and incident uterine cancer. J Natl Cancer Inst. 2022;114(12):1636-1645.
  3. Eberle CE, Sandler DP, Taylor KW, White AJ. Hair dye and chemical straightener use and breast cancer risk in a large US population of Black and White women. Int J Cancer. 2020;147(2):383-391.
  4. White AJ, Sandler DP, Gaston SA, Jackson CL, O’Brien KM. Use of hair products in relation to ovarian cancer risk. Carcinogenesis. 2021;42(9):1189-1195. doi:10.1093/carcin/bgab056.
  5. Agência Nacional de Vigilância Sanitária. Informe de Segurança GGMON nº 03/2025: Alisantes Capilares – Riscos, Cuidados e Alternativas Seguras. Brasília: Anvisa; 2025.
  6. Brasil. Agência Nacional de Vigilância Sanitária. Instrução Normativa IN nº 220, de 13 de abril de 2023. Estabelece a Lista de ativos permitidos em produtos cosméticos para alisar ou ondular os cabelos com requisitos para seu uso. Diário Oficial da União. 14 Apr 2023.
  7. U.S. Food and Drug Administration. Hair Smoothing Products That Release Formaldehyde When Heated. Silver Spring, MD: FDA.
  8. U.S. Office of Information and Regulatory Affairs. Use of Formaldehyde and Formaldehyde-Releasing Chemicals as an Ingredient in Hair Smoothing Products or Hair Straightening Products. RIN 0910-AI83. Unified Agenda; 2026. Accessed August 29, 2026.
  9. European Commission, Scientific Committee on Consumer Safety. Request for a scientific opinion on the safety of glyoxylic acid when used in cosmetic products. SCCS mandate approved April 30, 2026.

Read more from Dr. Estrada in the online version of this article at PracticalDermatology.com.

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