There are two main types of skin allergy. Contact dermatitis and Urticaria.
The cause of a Contact dermatitis is investigated by doing a Patch Test. The basic Patch Test will include the 43 most common triggers of contact dermatitis, suspended in Vaseline.
A Patch Test starts by patching these allergens on the patients back and leaving them in place for 48 hours. A contact dermatitis is revealed by a red bump appearing under the causative allergen within 36 to 96 hours.
The Patch Test is normally done on a Monday and the patient returns to the clinic on Wednesday and Friday to check for signs of contact dermatitis. The patches are removed on the Wednesday.
Once an allergy inducing substance is identified in this way it can be avoided.