The most common side effects of transdermal patches are mechanical reactions caused by applying or removing the transdermal patch, or by excessive perspiration under the patch. Allergic contact dermatitis (type IV allergic reaction) is the most commonly occurring hypersensitivity reaction and can be caused by the active substance or by excipients. Type I allergic reactions such as urticaria, bronchospasm and angioedema are rare and usually caused by the active substance in the patch. Allergy testing to determine the allergen is indicated following a type I allergic reaction, or after a type IV allergic reaction that requires an alternative for the patch. It is important to document hypersensitivity reactions in the electronic patient records in order to prevent a hypersensitivity reaction in the future.
