title: Photostability of commercial sunscreens upon sun exposure and irradiation by ultraviolet lamps.
abstract: BACKGROUND
  Sunscreens are being widely used to reduce exposure to harmful ultraviolet (UV) radiation. The fact that some sunscreens are photounstable has been known for many years. Since the UV-absorbing ingredients of sunscreens may be photounstable, especially in the long wavelength region, it is of great interest to determine their degradation during exposure to UV radiation. Our aim was to investigate the photostability of seven commercial sunscreen products after natural UV exposure (UVnat) and artificial UV exposure (UVart).
  
  
  METHODS
  Seven commercial sunscreens were studied with absorption spectroscopy. Sunscreen product, 0.5 mg/cm2, was placed between plates of silica. The area under the curve (AUC) in the spectrum was calculated for UVA (320-400 nm), UVA1 (340-400 nm), UVA2 (320-340 nm) and UVB (290-320 nm) before (AUCbefore) and after (AUCafter) UVart (980 kJ/m2 UVA and 12 kJ/m2 of UVB) and before and after UVnat. If theAUC Index (AUCI), defined as AUCI = AUCafter/AUCbefore, was > 0.80, the sunscreen was considered photostable.
  
  
  RESULTS
  Three sunscreens were unstable after 90 min of UVnat; in the UVA range the AUCI was between 0.41 and 0.76. In the UVB range one of these sunscreens was unstable with an AUCI of 0.75 after 90 min. Three sunscreens were photostable after 120 min of UVnat; in the UVA range the AUCI was between 0.85 and 0.99 and in the UVB range between 0.92 and 1.0. One sunscreen showed in the UVA range an AUCI of 0.87 after UVnat but an AUCI of 0.72 after UVart. Five of the sunscreens were stable in the UVB region.
  
  
  CONCLUSIONS
  The present study shows that several sunscreens are photounstable in the UVA range after UVnat and UVart. There is a need for a standardized method to measure photostability, and the photostability should be marked on the sunscreen product.
authors.affiliation: Department of Dermatology, Sahlgrenska University Hospital, SE-413 45 Göteborg, Sweden. helena.gonzalez@vgregion.se
authors.forename: Helena
authors.initials: H
authors.lastname: Gonzalez
authors.forename: Nils
authors.initials: N
authors.lastname: Tarras-Wahlberg
authors.forename: Birgitta
authors.initials: B
authors.lastname: Strömdahl
authors.forename: Asta
authors.initials: A
authors.lastname: Juzeniene
authors.forename: Johan
authors.initials: J
authors.lastname: Moan
authors.forename: Olle
authors.initials: O
authors.lastname: Larkö
authors.forename: Arne
authors.initials: A
authors.lastname: Rosén
authors.forename: Ann-Marie
authors.initials: AM
authors.lastname: Wennberg
mesh_terms: D019540:Area Under Curve; D004355:Drug Stability; D013053:Spectrophotometry; D013472:Sunlight; D013473:Sunscreening Agents / Q000737:chemistry*; D014466:Ultraviolet Rays
chemical_list: D013473:Sunscreening Agents