Hydroxyzine hydrochloride is a piperazine derivative, structurally based on a dimer of ethylenediamine and possessing antihistaminic and anticholinergic activity.
Risk factors
Positive patch-tests to ethylenediamine.
Clinical manifestations
Cutaneous: urticaria, eczema, fixed drug eruption (oral or genital mucous membrane, after 6 hours or more), systemic contact dermatitis (baboon syndrome, vesicular hand eczema, toxico derma-like rash).
Diagnostic methods
Cutaneous testing.
Patch-tests with hydroxyzine 2%, 5%, 10% aq.
M.I.F (macrophage migration inhibitory factor): positive in some cases of fixed drug eruption.
Drug re-challenge.
The drug may act as a hapten and bind to protein components or receptor cells of the lower dermis. This complex is similarly presented to the Langherans cells as in contact dermatitis (fixed drug eruption).
Cross-reactions among ethylenediamine, hydroxyzine, and cetirizine are influenced by sensitivity to diethylenediamine (common piperazinic ring).
Generally, patients sensitive to hydroxyzine are also sensitive to ethylenediamine.


  1. Stingeni L, Caraffini S, Agostinelli D, Ricci F, Lisi P, "Maculopapular and urticarial eruption from cetirizine", Contact. Dermatitis, 1997; 37 (5): 249-50
  2. Michel M, Dompmartin A, Louvet S, Szczurko C, Castel B, Leroy D, "Skin reactions to hydroxyzine", Contact. Dermatitis., 1997; 36 (3): 147-9
  3. Ash S, Scheman A.J, "Systemic contact dermatitis to hydroxyzine", Am. J. Contact. Dermat., 1997; 8 (1): 2-5
  4. Cohen H.A, Barzilai A, Matalon A, Harel L, Gross S, "Fixed drug eruption of the penis due to hydroxyzine hydrochloride", Ann. Pharmacother., 1997; 31 (3): 327-9

As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.