The Impact of Natural Sunlight Exposure on the UVB-Sun Protection Factor (UVB-SPF) and UVA Protection Factor (UVA-PF) of a UVA/UVB SPF 50 Sunscreen

February 2011 | Volume 10 | Issue 2 | Original Article | 150 | Copyright © 2011

Thomas J. Stephens PhD,a James H. Herndon Jr. MD FAAD,b Luz E. Colón MS CCRC CCRA,c Ronald W. Gottschalk MD FRCPCc

aThomas J. Stephens & Associates, Inc., Carrollton, TX bUniversity of Texas Southwestern Medical School and Dermatology Center of Dallas, Dallas, TX cGalderma Laboratories, L.P., Fort Worth, TX

Abstract

Objective: To compare the functional stability of Cetaphil® UVA/UVB Defense SPF 50 as measured by its ultraviolet B sun protection factor (UVB-SPF) and ultraviolet A protection factor (UVA-PF) values following exposure to natural sunlight versus the UVB-SPF and UVA-PF values of unexposed product.
Methods: These two randomized, controlled, evaluator-blinded, single-center trials were conducted according to the methods outlined in the 2007 Proposed Amendment to the Final Monograph, “Sunscreen Drug Products for Over-the-Counter Human Use.” Sunscreen samples were applied to glass plates and exposed to ultraviolet radiation in the form of natural sunlight in four minimal erythemal doses (MED) ranging from 2–16 MED (42–336 mJ/cm2). Three test sites were identified on the back of each study subject. Exposed sunscreen (one of four doses), unexposed sunscreen, and a UVB-SPF 15 control sunscreen were applied to the three test sites in a randomized fashion, followed by UV irradiation of incremental doses. Erythema and pigment darkening responses were assessed immediately following UV exposure and again 16–24 hours (erythema) or three to 24 hours (pigment darkening) after exposure. UVB-SPF and UVA-PF values were calculated for the exposed and unexposed samples.
Results: The calculated UVB-SPF and UVA-PF values for all test samples (exposed and unexposed) were >50 and >9, respectively, which were greater than the stated UVB-SPF and UVA-PF values on the product label. No differences were observed between the exposed and unexposed samples in UVB-SPF or UVA-PF.
Conclusion: The UVA and UVB protection using standard evaluation techniques of Cetaphil UVA/UVB Defense SPF 50 remains stable despite exposure of the sunscreen to natural sunlight containing UVB ranging from 2–16 MED (41–336 mJ/cm2) and coexistent UVA.

J Drugs Dermatol. 2011;10(2):150-155.

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Introduction

The acute and chronic dermatologic complications from the ultraviolet (UV) component of sunlight are well characterized. Among other complications, exposure to UV radiation from sunlight is associated with approximately 90 percent of non-melanoma skin cancer cases,1 approximately 65 percent of melanoma cases1 and approximately 90 percent of the cosmetic changes attributed to aging.2,3 The UV radiation causing these dermatologic complications falls in the UVB (290–320 nm) and UVA (320–400 nm) wavelengths. Various organic and inorganic UV filters have been identified to protect against the spectrum of UV radiation through mechanisms of absorption, reflection or diffusion, or a combination thereof.

Although sunscreens are generally considered effective for protecting against photocarcinogenesis,4 photoimmunosuppression5 and photoaging,6 concern has been expressed that certain UV filters may lose part of their protective capability following exposure to UV radiation.7–16 Certain filters are known to degrade with exposure to UV; however, relatively little has been reported on the effectiveness of UV-irradiated sunscreen formulations in protecting skin against damage from UVB and UVA.

The U.S. Food and Drug Administration's (FDA's) proposed amendment to the final monograph on "Sunscreen Drug Products for Over-the-Counter Human Use" includes new provisions to help ensure that sunscreen products remain effective over typical periods of exposure.17 These provisions call for pre-irradiation of sunscreen prior to assessing the UVB sun protection factor (UVB-SPF) and UVA-protection factor (UVA-PF).17 The purpose of the two studies described herein was to evaluate the UVB-SPF and UVA-PF of a commercially available sunscreen formulation, Cetaphil® UVA/UVB Defense SPF 50 (Galderma Laboratories, L.P., Fort Worth, TX), that has been exposed to UV radiation in the form of natural sunlight.

Methods

Study Population
Men and women 18 years or older in general good health, as determined by a health questionnaire, were eligible for participating in these studies if they had Fitzpatrick skin type I, II or III (UVBSPF study) or type II or III (UVA-PF study). Individuals who were instructed by a healthcare professional to avoid sunlight due to a medical condition or medication contraindication were excluded from participation. Other major exclusion criteria included known abnormal response to sunlight; known hypersensitivity to sunscreens; observable suntan, scars or active cutaneous lesions on areas of the back to be tested; or any disease or condition that the study investigator deemed inappropriate for participation.

Although sunscreens are generally considered effective for protecting against photocarcinogenesis, photoimmunosuppression and photoaging, concern has been expressed that certain UV filters may lose part of their protective capability following exposure to UV radiation. Certain filters are known to degrade with exposure to UV; however, relatively little has been reported on the effectiveness of UV-irradiated sunscreen formulations in protecting skin against damage from UVB and UVA.

Study Design and Conduct
These were randomized, controlled, evaluator-blinded, single- center trials. The study protocols were approved by an Institutional Review Board, and the studies were conducted in accordance with Good Clinical Practice Guidelines. Written informed consent was provided by the enrolled participants.

The test product for these two studies was Cetaphil UVA/UVB Defense SPF 50, which has the following active ingredients: octinoxate (7.5%), octisalate (5%), octocrylene (7%), oxybenzone (6%) and titanium dioxide (5.7%). The UVB-SPF and UVA-PF values on the label for this product are 50 and 9, respectively (Data on File, Galderma Laboratories, L.P.).

Both studies were conducted according to the procedures as described in the 2007 Proposed Amendment (21 CFR Parts 247 and 252) to the Federal Register 64 (98), entitled "Sunscreen Drug Products for Over-the-Counter Human Use."17 Prior to the start of each study, a thin film of sunscreen (2 mg/cm2) was appliedto a glass plate and exposed to UV radiation in the form of natural sunlight to approximately the following levels of minimal erythemal dose (MED)–2 MED (42 mJ/cm2), 4 MED (84 mJ/cm2), 8 MED (164 mJ/cm2) or 16 MED (336 mJ/cm2) of UVB and the associated UVA. Exposures occurred on 02/04/09, 02/05/09, 02/11/09, 02/18/09 and 02/19/09 between 11:00am and 4:00pm in Dallas, TX; noontime MED levels during this time of year range from 1.5–2.0 MED/hour. UVB radiation was monitored using a Solar Light PMA 2100 detector (Solar Light Company, Inc., Glenside, PA) with a PMA 2101 SUV detector calibrated for 21 mJ/cm2 (erythremically effective dose). UVA radiation was measured using a Solar Light PMA 2100 detector with a PMA 2110 SUV detector. Following exposure, sunscreen was removed from the glass plates and stored in photo-protected vials under refrigeration.

Eligible subjects were assessed for their inherent (unprotected) MED associated with UVB exposure and minimal pigment darkening (MPD) dose associated with UVA exposure. For determining the unprotected MED and MPD, each subject received at least five irradiation exposures on adjacent unprotected skin sites on the lower back. Each exposure represented a 25 percent increase in energy over the previous exposure. UV radiation was provided using a single-port solar simulator with a 150-watt xenon arc lamp (Model 16S Solar UV Simulator, Solar Light Company, Inc.), with UG-11 and WG-320 filters (Schott Glass, Inc., Elmsford, NY) providing UVA and UVB radiation, respectively. The light source was placed 6.5 cm from the test sites, and the UVA and UVB radiation exposure was measured using the 3D-600 meter (Solar Light Company, Inc.). The sites were examined by a clinical grader for immediate erythema (MED) and immediate pigment darkening (MPD) after the completion of each exposure.

Erythema was assessed approximately 16–24 hours after UV exposure using a 4-point scale (no erythema, questionable response/unclear, erythema extending to the borders and erythema with or without edema present). The site receiving the lowest dose of UV radiation that produced erythema extending to the borders was selected as the unprotected MED for that subject. Pigment darkening was assessed approximately three to 24 hours after UV exposure using a similar 4-point scale (no pigment darkening, questionable response/ unclear, darkening over essentially the entire test site and definite darkening over the entire test site). The site receiving the lowest dose of UV radiation that produced darkening over essentially the entire test site was selected as the unprotected MPD for that subject.

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