H2-blockers (cimetidine, famotidine, etc) can be used to treat skin allergies.

  Urticaria or "hives" is primarily caused by the release of histamine in response to an allergen...and most of this histamine activity is mediated by h1 receptors in the skin's blood vessels.

  Hence the mainstay of therapy for acute urticaria is an H1-receptor antagonist...Zyrtec, Claritin, chlorpheniramine, etc.

  But there's some evidence that adding an H2 receptor antagonist is sometimes more effective than an H1 blocker alone.