As many as 415 million people worldwide may have rosacea, according to new research in the British Journal of Dermatology.

Dr. Jacob Thyssen and colleagues at the University of Copenhagen, Denmark, conducted a systematic review of population-based studies that included information on the incidence and prevalence of rosacea. Data was collected from 32 studies around the world, comprising 26.5 million patients. The proportion with rosacea in the individual studies ranged from 0.09 percent to 22.41 percent, and when the studies were pooled together, the proportion was 5.46 percent, which translates to 414,960,000 rosacea sufferers worldwide. 

However, depending on how the researchers obtained the data, the proportion of rosacea sufferers varied significantly. The prevalence of rosacea was highest when self-reported, with a rate of 9.71 percent (737,960,000), while the rate of dermatologist-diagnosed rosacea was 5.53 percent (420,280,000).

“Many factors may contribute to the difference in estimates,” Dr. Thyssen says in a news release. “While many more people may self-diagnose rosacea than are actually suffering from the condition, correct diagnosis by a physician may depend on the physician’s experience as well as the patient’s appearance at the time of the exam.”

Dr. Thyssen and colleagues said further research will be needed to more precisely determine the number of rosacea patients worldwide. Although no epidemiological studies have been published in the United States, the National Rosacea Society has estimated the number of Americans with rosacea to be more than 16 million, based on a 5 percent prevalence rate determined by analysis of worldwide studies and the ethnic composition of the population nationwide.

“Despite being a relatively common skin condition, only around 18 percent of Americans with rosacea are believed to be currently under medical treatment for their condition,” says Dr. John Wolf, chairman of dermatology at Baylor College of Medicine in Waco, Texas, in a news release. “Many of those with milder rosacea may not even realize they have a disease that can be treated, instead using over-the-counter skin care products or covering their redness with makeup. However, there are now more medical therapies available for rosacea’s signs and symptoms than ever before, even for mild cases.”