Alcohol vehicles in tests for non-immunological immediate contact reactions

In a search for vehicles that might enhance the sensitivity of human skin tests for nonimmunological immediate contact reactions, benzoic acid was tested in 17 liquid vehicles on 16 medical students using the open application test method on the upper back. The results were read visually and the change in blood flow was measured using a laser-Doppler flowmeter 20, 40 and 60 min after application of the test substances. 2-propyl alcohol (isopropanol), ethyl alcohol (ethanol), 1,2-propylene glycol and water were mixed to form alcohol, alcohol/water, alcohol/alcohol, alcohol/propylene glycol and propylene glycol/water vehicles. The reactions were stronger in the alcohol/water vehicles than in the alcohols as such. The addition of 25% propylene glycol to isopropanol and ethanol had the greatest enhancing effect on the reactions. Ethanol has been the most popular liquid vehicle in tests for non-immunological immediate contact reactions, but at least with benzoic acid, stronger reactions can be elicited if alcohol/propylene glycol or alcohol/water mixture are used.