A series of experimental
sunscreen preparations based on a common vehicle, containing increasing concentrations of either octyl-N-dimethyl-
p-aminobenzoate (o-
PABA) or
2-ethylhexyl-p-methoxycinnamate (2-EHMC) as the ultraviolet B (UVB) absorber, has been tested in the hairless mouse for the ability to protect from
erythema, from the systemically suppressive effects of UVB (280-320 nm) radiation on
contact hypersensitivity, and from photoisomerization of epidermal
urocanic acid. All the preparations protected efficiently from the
edema component of the
erythema response when mice were exposed to UVB radiation equivalent to three times the minimal
erythema dose (MED). However, when mice were exposed to UVB radiation equivalent to 15 x MED, protection from
erythema was observed only at the higher concentrations of each UVB absorber (10% 2-EHMC and 10% or 15% o-
PABA). Protection from the UVB-induced suppression of
contact hypersensitivity was shown to be dependent on both the nature of the UVB absorber and its concentration. Photoimmunoprotection by the
sunscreens containing 2-EHMC was evident at lower concentrations (5% and 10% 2-EHMC) than with o-
PABA, following both 3 x MED and 15 x MED of UVB exposure. Photoimmunoprotection by o-
PABA-containing
sunscreens was observed only at 15% o-
PABA following 3 x MED, and failed at all tested concentrations after 15 x MED of UVB exposure. Regardless of the photoimmunoprotective capacity,
sunscreen preparations containing either of the UVB absorbers prevented the UVB-induced formation of cis
urocanic acid in the mouse epidermis and in vitro under all conditions tested. Thus, there appeared to be a correlation between protection from
edema and from cis
urocanic acid formation at 3 x MED of UVB, but a dissociation of these variables at 15 x MED of UVB. There was no relation apparent at either UVB dose between either
edema or cis
urocanic acid formation and protection from suppression of
contact hypersensitivity.