Edward Marlowe

A comparison of in vivo and in vitro testing of sunscreening formulas.

Abstract— Seven commercially available sunscreens were compared by three different methods. Absorbance spectra were measured for each product in isopropanol solution and also on hairless mouse epidermis. In vivo tests were performed on human volunteers using a Xe arc solar simulator. Sun Protection Factors (SPF) were calculated by each method for each product tested and the results compared. By all methods used, the combination of 7% octyl dimethyl para‐aminobenzoic acid and 3% oxybenzone provided the most protection from U.V. light. While estimates of the effectiveness of all products were much too high when calculated by the isopropanol solution method, the hairless mouse epidermis technique seems to be an accurate tool for predicting product efficacy in vivo.

Skin type, minimal erythema dose (MED), and sunlight acclimatization

Minimal erythema doses (MEDs) of individuals with different skin types were compared. Each skin type was shown to be statistically different from each other skin type in terms of sunburn sensitivity. Individuals of each skin type who primarily stayed indoors were compared with those who attempted to be outdoors. In the winter there was no difference between the sunburn sensitivity (MEDs) of these groups. During the summer, those who went outdoors were more resistant to sunburn than those who stayed indoors. In effect, acclimatization makes an individual respond to sunlight like a less sensitive skin type. However, acclimatization appears transitory, and benefits can be lost within a month or two.

Sunscreen protection against drug-induced phototoxicity in animal models.

Abstract Phototoxicity was induced in animal models by photoreactive drugs in order to test sunscreen efficacy. In combination with uv-A irradiation, 8-methoxypsoralen and to a lesser extent chlorpromazine and demeclocycline elicited cutaneous erythema, edema, and ulcerative lesions in mice and guinea pigs. A commercial preparation of 5% para-amino-benzoic acid (PABA) in alcohol with proven effectiveness in preventing normal sunburn failed to protect against phototoxic drug reactions. An experimental, broad-spectrum sunscreen, PL-254—containing esters of PABA and benzophenone-blocked virtually all phototoxic response to all three drugs. Absorbance spectra of the PABA product and of PL-254 in solution and on the skin of hairless mice confirmed that PABA absorbs uv energy primarily in the uv-B range while PL-254 absorbed both uv-A and uv-B radiant energy. The uv absorbance spectra of both products on skin differed significantly from their spectra in solution.

P-aminobenzoic acid as a sunscreen and its behaviour on the skin

PABA (p‐aminobenzoic acid), a highly regarded sunscreening agent, has recently been shown to exhibit different absorption characteristics when applied to excised hairless mouse epidermis than when in dilute alcoholic solution. In the present study the cause of the differences was investigated.

Commentary on 'UVB-SPF': the SPF labels of sunscreen products convey more than just UVB protection.

The FDA recently published a proposed amendment of the Final Monograph for OTC Sunscreen Products. Among the proposals, FDA revised solar simulator performance specifications and additional labeling for sunscreen products. The maximum allowable labeled sun protection factor (SPF) was increased to SPF 50 while simultaneously requiring it to be called ‘UVB‐SPF’. UVB accounts for 80–91% of the erythemic effectiveness of the UV solar simulator specified in the amendment. Analysis of the specified solar simulator spectrum used to determine SPF indicates that if 100% of the UVB is blocked, it is mathematically impossible to achieve an SPF in excess of ∼11 without also blocking at least some UVA. Consequently significant UVA protection must be provided for sunscreen products to achieve SPFs of 15 and higher. At the maximum allowed SPF 50, where only 2% or less of the effective UV risk remains, the minimum reduction of UVA erythemal effectiveness must by definition be 78–90%. While mandating UVA protection criteria is doubtless important, especially as it relates to sunscreen photostability, there is no utility in, or basis for, the proposed ‘UVB‐SPF’ descriptor as existing high SPF labeling indicates both UVB and UVA protection.