Four cases of allergic contact sensitivity to alkyl esters of p-hydroxybenzoic acid (parabens) were detected during routine closed patch tests on 91 patients with contact dermatitis. All four patients had refractory dermatitis of unknown cause and all were using topical medications containing parabens as preservative. Cross-sensitivity was demonstrated in additional tests with parabens in a concentration of 5%. Positive reactions to p-hydroxybenzoic acid were also obtained by patch test (one patient) and by intradermal injection (one patient).
Wuepper KD. Paraben Contact Dermatitis. JAMA. 1967;202(7):579–581. doi:10.1001/jama.1967.03130200065010