Ultraviolet protective performance of photoprotective lipsticks: Change of spectral transmittance because of ultraviolet exposure

Abstract

Background: Photoinstability of sunscreens because of ultraviolet (UV) exposure is a well-known and common phenomenon. Recently, it was also shown that sunscreens with complex filter combinations are photo-inactivated by UV exposures, which can easily be acquired by solar exposure over several hours. Objectives: To assess the change of the spectral transmission after UV exposure (UV-challenged protective performance) of 27 commercially available photoprotective lipsticks. Methods: Quartz slides were covered with a lipstick layer (area density 1.0 ± 0.1 mg/cm2 ) and irradiated with increasing doses of solar-simulated radiation. The spectral transmission (T) was measured spectrophotometrically before and after 5, 12.5, 25, and 50 standard erythema doses (SED) of exposure. We calculated the change in transmission (photoinstability) as the difference between the spectral transmission before and after a defined UV exposure, ΔT, and the arithmetic mean, for both the UVA (ΔTA) and UVB (ΔTB) ranges. A product was labelled as photounstable if the mean photoinstability in the UVA, ΔTA, or UVB range, ΔTB, was higher than 5% for an UV exposure of 12.5 SED. Results: Eleven products showed a significant photoinstability in the UVA range (ΔTA between 6% and 27%), only one product in the UVB range (ΔTB = 13%), and one product in both the UVA (ΔTA = 31%) and UVB (ΔTB = 9%) range. In one product photoinstability became significant in the UVA range at higher UV exposures. Conclusions: Out of 27 lipsticks only 13 products showed a photostable performance (ΔTA<5% and ΔTB<5% for 12.5 SED). We propose therefore that only products, which fulfil these UV photostability criteria should be marketed. Copyright © Blackwell Munksgaard 2005.