Assessment of thickness of photoprotective lipsticks and frequency of reapplication: results from a laboratory test and a field experiment

Summary Background The thickness of the sunscreen layer that is actually applied by consumers under usual conditions has been determined for photoprotective lotions and creams; however, this question is still unanswered for photoprotective lipsticks. Objectives To assess lipstick thickness (area density) and frequency of application per day for two commercially available photoprotective lipsticks with different consistency. Methods The study consisted of a laboratory test and a field experiment. In the laboratory test the applied lipstick thickness was determined as area density in mg cm−2 for a group of 28 panellists under standardized conditions. In a separate group of 18 subjects we assessed the area density and the frequency of application per day for two photoprotective lipsticks during a 6‐day skiing course. Results In the laboratory test the median and 95% confidence interval of the area density was 0·98 mg cm−2 (0·66–1·65) and 0·86 mg cm−2 (0·63–1·40) for products A and B, respectively. The respective values of the field experiment were 1·58 mg cm−2 (0·79–2·23) (product A) and 1·76 mg cm−2 (1·16–3·50) (product B). Only 11% of all applications of lipstick A and 6% of all applications of lipstick B reached the reference area density of 2·0 mg cm−2. The difference between the median of the area density for lipstick A (firm consistency) and lipstick B (soft consistency) was not statistically significant. No statistically significant influence on the area density was found for age, sex, photobiological skin type or regular lipstick use. The median daily frequency of application was 2·2 times for lipstick A and 3·0 times for lipstick B. Conclusions Our investigation shows that photoprotective lipsticks are applied in a much thinner layer than recommended by international standards (2 mg cm−2). This results in a significant reduction of the photoprotective capacity. Furthermore, the frequency of application is too low for adequate protection. Therefore, we propose that the sun protection factor (SPF) should be assessed for an area density that reflects the actual usage patterns. As long as the test protocol is not adapted to the reduced area density, photoprotective lipsticks with high and ultrahigh SPF should be recommended, especially for individuals with increased risk for the development of lip malignancies.