Persistent rashes can be caused by a contact allergic dermatitis to chemicals with which the skin has regular exposure. This can include personal hygiene products, clothing and occupation-related materials. Allergy patch testing involves the application of individual, standardized allergens to the upper back for 48 hours. After a subsequent 24 hours, the back is re-evaluated. Reaction to a particular allergen may suggest the cause for the rash. Counseling is provided on how to avoid this chemical in the future.