Propylene glycol is used in foods, medicine and cosmetics because it is a good solvent which has, simultaneously, moisture-regulating, antiseptic, and preservative effects. Propylene glycol may produce eczematous skin reactions of toxic and, more rarely, of allergic nature. Positive patch test reactions to propylene glycol are difficult to interpret. Allergic reactions may be confirmed by a clear clinical relevance, repeated local skin provocation (usage test), or oral provocation. In the Department of Dermatology, University of Oregon, 84 patients were patch tested with 100% propylene glycol. Five of 12 patch test-positive patients had allergic reactions while seven had irritant reactions. In the Department of Dermatology, Gentofte Hospital, 248 consecutive eczema patients were patch-tested with propylene glycol in concentrations of 100%, 20%, and 2% in water. Two of five patients with positive reactions to patch tests showed an itchy eczematous eruption after oral provocation with 15 ml propylene glycol. Skin reactions due to propylene glycol are rare and should not bring the preparation into unnecessary discredit. The possibility of propylene glycol allergy should be recognized by dermatologists as propylene glycol is used in local steroids and other topical preparations.