Kesten and Slatkin1 confirm the work of Rothman and Rubin2 on the excellence of paraaminobenboic acid as a sunscreen. Rothman, in discussing this paper, comments on the difficulty of making smooth creams with the free acid.
For some time, I have been using the following cream, which is a smooth elegant preparation of 15% paraaminobenzoic acid. It consists of 4.5 cc. of paraaminobenzoic acid, 6.0 cc. of distilled water, 6.0 cc. of hydrophilic ointment, and add vanishing cream to make 30.0 cc.
The pharmaceutical instructions are as follows: Levigate the paraaminobenzoic acid with water to a smooth paste. Add hydrophilic ointment, and finally add the required amount of vanishing cream. The vanishing cream used may be that of any reputable cosmetic firm.
As Rothman points out, this preparation is an excellent sunscreen and it is much less sensitizing than the esters of paraaminobenzoic acid.
FISHER AA. PARAAMINOBENZOIC ACID AS A SUNSCREEN. AMA Arch Derm Syphilol. 1953;68(6):728. doi:10.1001/archderm.1953.01540120112016