Tanning without preceding erythema was induced by administering 15 minimal erythmal doses (MEDs) of solarsimulating radiation, three times on alternate days to white skin pretreated with 40 μl/sq in of a 5% hydroalcoholic solution of aminobenzoic acid. Tanning obtained through this chemical filter was compared clinically and histopathologically to that which followed the sunburn reaction induced by 3 MEDs, three times on alternate days.
Sunburn tan was preceded by marked epidermal injury; most newly formed pigment was in coarse clumps within the malpighian cells with little in melanocytes. Epidermal damage was insignificant with aminobenzoic acid mediated tans. The pigment granules were finely dispersed in keratinocytes, and melanocytes had an abundance of granules. In both instances, melanocytes increased in number, size, and enzymic activity.
Langner A, Kligman AM. Tanning Without Sunburn With Aminobenzoic Acid-Type Sunscreen. Arch Dermatol. 1972;106(3):338-343. doi:10.1001/archderm.1972.01620120026005