Cosmeceuticals: Sunscreens

Repeated exposure to ultraviolet (UV) light can be directly correlated to premature facial aging, the development of cancerous lesions, immunosuppression and matrix degradation. Just one blistering sunburn in adolescence can double the risk of developing skin cancer later in life, making broad spectrum sun protection arguably the most important product in one's daily care regimen.¹ Understanding the parameters surrounding the FDA's final ruling on sunscreen products; the variety of sun protection ingredients available; why combining chemical and physical sunscreen ingredients offers the most protection; and how added antioxidants can improve the overall efficacy of sunscreen products will ultimately allow the professional to make more informed recommendations regarding the use of sunscreen.

FDA SPF RECOMMENDATIONS

As outlined in the FDA Final Rule of 2011, sunscreen products claiming to provide broad spectrum protection against both UVA and UVB are required to protect against a critical wavelength of at least 370nm (the mean level must be equal to or greater than 370nm).² Protection against this wavelength is rather difficult to attain but will ensure that sunscreen products meeting this threshold provide a substantial amount of broad spectrum protection.

Presently, only four of the ingredients approved by the FDA provide true broad-spectrum protection when used at appropriate levels: zinc oxide, titanium dioxide, avobenzone, and ecamsule. For this reason, a broad spectrum sunscreen following the FDA's sunscreen monograph should include one of those four ingredients in addition to UVB-protecting ingredients.³

The consumer population often misunderstands how sun protection factor (SPF) plays a role in their sunscreen products. SPF value specifies the level of sunburn protection of that particular product. This calculation takes into account the ratio of time it takes to obtain sunburn with sunscreen divided by the time it takes to burn without sun protection.⁴ However, this value only indicates protection from the sun's burning rays, or UVB, and does not factor in the aging rays emitted by UVA. This misunderstanding often leads to patients purchasing sunscreen products with high SPF, thinking they are thoroughly protected. In actuality, a SPF of 15 protects from 93 percent of UVB rays, SPF 30 protects from 97 percent, and a SPF 60 protects from 98 percent.⁵ It is important to clarify with patients that this number has no bearing on how much protection against UVA rays a product provides, if any.

In most cases, the higher the SPF, the thicker and more opaque the product becomes, making it less appealing to the patient. Having patients wear an SPF 30 in a cosmetically elegant sunscreen product that they will be more likely to wear daily is preferable to providing them with a high SPF, thicker in consistency, that they will probably not be compliant with daily. Given that nearly all sun protection products break down when exposed to UV light, re-application every two hours is imperative.⁵

Waterproof and sweat-proof claims are false and are against the FDA's Final Rule. At this time, there are no waterproof or sweat-proof products available on the market. Since these terms are misleading to the patient, sunscreen manufacturers are no longer able to make such claims. However, products can be tested for water or sweat resistance, meaning they are capable of protecting from UV exposure while in dynamic water or while sweating for up to either 40 or 80 minutes.^3,6 Regardless of a product's claims, all sunscreens should be reapplied after swimming, sweating, toweling off, or vigorous outdoor activity.³

PHYSICAL VS. CHEMICAL AND THE BENEFITS OF COMBINING

It is important to understand the range of sun protection ingredients available and currently approved by the FDA to make informed recommendations concerning the effective selection and use of sunscreen products. Sunscreens can contain either chemical or physical ingredients, or a combination of both. As mentioned, it is critical to the health of the skin that the sunscreen product protects against both UVA and UVB wavelengths. It is widely known that UVB rays are the primary cause of sunburn while UVA rays' longer wavelength gives them the ability to penetrate into the dermis, breaking down the extracellular matrix (ECM) and resulting in premature aging.

PHYSICAL SUNSCREEN INGREDIENTS

A physical sunscreen agent filters UV light by scattering or reflecting the photons before they are able to impose damage at the cellular level.⁷ Although a highly effective means of sun protection, physical sunscreen agents are often thick, leaving a white, opaque appearance on the skin.⁸ Advances in technology have allowed for micronized sunscreen particles, which have demonstrated the ability to scatter UV light while providing a cosmetically elegant finish.⁷

Zinc oxide offers broad-spectrum protective benefits with a high safety and stability profile. It is considered the more wearable of the physical sunscreens, as zinc formulas typically cause less of a white appearance on the skin compared to titanium dioxide. Micronized zinc is naturally anti-inflammatory, which gives it additional benefits when used to prevent the erythema of sun exposure.⁹

Titanium dioxide is an inert sunscreen ingredient with no record of photosensitization. The large particle sizes of titanium dioxide can leave a white hue on the skin when applied, limiting their use in darker-skinned patients. Titanium dioxide, like zinc oxide, is often formulated with micronized particles to overcome this cosmetic concern.¹⁰

CHEMICAL SUNSCREEN INGREDIENTS

Chemical sunscreens are organic substances capable of penetrating the dead corneocytes to absorb UV rays before they are able to enter the skin. Consumer fears surrounding chemical sunscreen ingredients are typically misdirected, as most reactions are due to the base of a product rather than the sunscreen agent ingredients themselves.^11,12

Octisalate is part of the salicylates family, which also includes homosalate (homomenthyl salicylate) and trolamine salicylate. These UVB sunscreen agents offer photostability and are considered non-sensitizing, making them a favorable choice from a formulation stand point. Although often thought of as a weak sunscreen agent, octisalate maintains an excellent safety profile that contributes to its continued use in the skin care industry.⁷ Due to its weak UVB protection, it is often combined with other chemical or physical sunscreen agents.

Octinoxate falls under the family of sunscreen ingredients called cinnamates. Cinnamates are the most widely used chemical sunscreen agents on the market as they do not stain clothing, are the least likely to cause an allergic reaction, and provide excellent protection.^8,13

COMBINATION IS KEY

The combination of both physical and chemical sunscreen agents provides the most cosmetically elegant formulas. This is imperative for consistent patient compliance. A combination of physical and chemical sunscreen ingredients also provides the most effective coverage across the entire UVA and UVB spectrums. When antioxidants are incorporated into a formulation, the end result is a superior sunscreen product that protects against UV damage while quenching reactive oxygen species (ROS) and reducing cellular oxidation.^14,15

Antioxidants are now used in many sunscreen formulations for an additional layer of protection. It is common knowledge that topical sun protection products cannot protect against all UV rays, especially UVB rays that create ROS. Currently there is not a sunscreen ingredient capable of reflecting or absorbing all UV light, therefore antioxidants can be added to enhance protection.

Perhaps the most pertinent antioxidants for sun protection products are those that exhibit chemo-preventative properties. Numerous studies have been conducted concerning the shielding benefits of topical antioxidants, and results specify that the addition of antioxidants to daily sunscreen usage may be as important to the prevention of skin cancer and premature signs of aging.^16-18 The following antioxidants are known ROS scavengers and also demonstrate chemo-preventative qualities.

Multiple studies have indicated that topically administered epigallocatechin gallate (EGCG), found in green tea, demonstrates apoptosis in tumors, while also inhibiting UVB-induced carcinogenesis when taken orally.¹⁹

Resveratrol, found in grape extracts, has demonstrated the ability to act on cellular signaling mechanisms related to UV-mediated photoaging, including MAP kinases, nuclear factor kappa B and matrix metalloproteinases. ²⁰

The anticarcinogenic effect of genistein, found in soybeans, remains unclear, but it is known that it is a strong inhibitor of tyrosine kinases, which are responsible for phosphorylating proteins essential for the regulation of dividing cells.²¹

Studies have demonstrated that low doses of topical silymarin, found in milk thistle, could almost entirely inhibit the effect of tumorogenesis by forcing UVB-induced sunburn cells into apoptosis.²¹

Similar to silymarin, caffeine also forces UVB-induced sunburn cells into apoptosis in the epidermis when given orally and applied topically.²²

Although a welcome addition to any sunscreen formulation, it must be noted that antioxidants are in no way an alternative means of sun protection. It is crucial to apply a broad spectrum sunscreen product at least 30 minutes prior to sun exposure. Preliminary studies have only just begun to show the benefit of combining sun protection products and antioxidant ingredients, but thus far indicate that the addition of antioxidants may provide added benefit.

Daily application of a broad spectrum sunscreen product is imperative for overall health of the skin. Helping patients understand the FDA's 2011 Final Rule on how sunscreen products are labeled will ultimately help them make informed decisions about sunscreen products, while also protecting against lofty and often unrealistic claims. For the most cosmetically elegant sunscreen formulation, a combination of physical and chemical sunscreen agents is recommended. This minimizes the thick feel of a physical sunscreen while also providing protection against the entire UV spectrum. Finally, incorporating chemopreventative antioxidants into sunscreen formulations seems to be the wave of the future and has shown to have considerable effects on UVB-induced sunburn cells.

Jennifer Linder, MD is a dermatologist and Mohs micrographic skin surgeon, serving as Chief Scientific Officer for skin care and chemical peel company PCA SKIN, and running a private practice out of Scottsdale, AZ. She holds a clinical faculty position in the Department of Dermatology at the University of California San Francisco. Dr. Linder is a spokesperson for The Skin Cancer Foundation and sits on the Editorial Board of the Cosmetics Journal. She has been frequently interviewed by the press and published in trade publications, journals and textbooks, most recently “A Practical Guide to Chemical Peels, Microdermabrasion & Topical Products” by Rebecca Small, Dalano Hoang and Jennifer Linder; and the chapter “Cosmeceutical Treatment of the Aging Face” in “Aesthetic Medicine: Art and Techniques,” edited by Peter M. Prendergast and Melvin A. Shiffman.

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