Allergic contact response to vitamin A acid.

Three patients treated daily with vitamin A acid cream experienced after one week, seven weeks and 14 weeks respectively sudden redness and itching at the treated sites. Patch testing with the cream (containing 0.05% vitamin A acid) and with vitamin A acid 0.05% in absolute alcohol produced strongly positive reactions in the patients but only slight erythema in some of the controls. Since patch testing with vitamin A acid 0.005% in absolute alcohol elicited no response in controls but positive reactions in the three patients, it is probable that these latter reactions were due to contact allergy. Histologically the test reaction showed intact epidermis and dense dermal infiltration by mononuclear cells, and thus resembled a response of the tuberculin type.