Antihistamines to be taken by mouth – medications like Benadryl® and Atarax® – are commonly used to combat itch. Although they are very effective in the treatment of itchy hives (‘urticaria’), all too often these drugs are not very successful in alleviating the itch of common, inflammatory skin disorders, such as ‘atopic dermatitis’ (eczema) or psoriasis. And antihistamines frequently cause drowsiness as a side effect, which can be particularly troublesome in the elderly.
But now there is evidence that there are other benefits besides relief of itch when they are used to treat these inflammatory skin conditions. We have now shown that topical antihistamines – that is, when applied directly to the skin – improve barrier function and reduce inflammation in mouse models of atopic dermatitis. Both H1 and H2 antihistamines were effective, but by somewhat different mechanisms. Topical antihistamines should have fewer side-effects than oral delivery, because absorption into the blood should be lower. But sedation can still occur if the agents are very potent, like doxepin (or Zonalon®), or if they are applied in large amounts and/or to a large percentage of the body surface, even if they are less potent forms, like diphenhydramine (or Benedryl®).
Bottom line: If topical formulations of antihistamines that do not produce drowsiness become available commercially, they could be a promising addition to the treatment of skin disorders characterized by inflammation and a skin barrier defect, such as atopic dermatitis or psoriasis. However, further study is still needed to determine their role in treating inflammatory skin diseases and which class of antihistamines would be most effective.