The T.R.U.E. Test is the best starting place to determine if a person has a contact allergy to a substance or preservative (an allergen). The T.R.U.E. Test is FDA approved. This involves placing small patches of potential allergens on the skin and watching in the following days for skin reactions that would indicate an allergy. When positive to an allergen, detailed information is given to help patients know how to detect and avoid contact with that allergen.