Although much less common than irritant dermatitis, allergic contact dermatitis is still an important source of problems for many people. As the name suggests, this type of reaction is not a simple matter of direct irritation but is a true allergic condition mediated by the skin's complex immune system. While allergic contact dermatitis can be produced by just about any substance, some agents are more likely to trigger it than others. Poison ivy dermatitis, nickel allergy, and latex allergy are three well-known examples of allergic contact sensitivity that can serve to illustrate many of the main aspects of allergic contact skin conditions.
Poison Ivy Dermatitis
The term poison ivy is misleading. The milky saplike resin, called a catechol, that is responsible for the rash of this condition and that of its relatives, poison sumac and poison oak, is not a poison at all but a true allergen. In the United States, the overall incidence of allergy to the poison ivy family of plants is estimated to be between 50 percent and 75 percent of the population.
Sensitization (the immunologic reactions that establish allergy) generally requires a week to two weeks. While some people become allergic to these plants following their first exposure to the resin, many others do not. In fact, it often takes numerous exposures before the allergy develops. However, once sensitization is complete, subsequent reexposures to the poison ivy resin generally result in symptoms in a much briefer period, usually somewhere between five and seventy-two hours after contact.
The extent and severity of poison ivy reactions depend in large measure on how much of your skin comes in contact with the resin, how much is deposited on the skin, and how innately sensitive you are to it. In other words, the more allergic to poison ivy you are and the more of the sap you get on you, the worse your reaction will be. Typical symptoms consist of intense redness, swelling, and blistering at the sites of contact. Occasionally, the allergic reaction can be quite severe and debilitating. Because the poison ivy vines or shrubs tend to brush up against you as you pass, the blisters and the rash are typically distributed in a streaklike or linelike fashion along the skin.
Patients with poison ivy invariably become concerned about spreading their condition to others. Since the reaction is an allergy, not an infection, the concern is happily unfounded. You cannot spread your allergy to someone else, not even if they come in direct contact with the blister fluid itself. Should the blisters open, however, the possibility of secondary bacterial infection increases, and you need to be especially careful at that point because the infection (not the allergy) can be spread to others.
Prevention is the best form of treatment for poison ivy dermatitis. This means wearing protective clothing gloves, long-sleeved shirts, and long pants, for example when gardening or hiking. Several recently introduced barrier creams can also be useful. These include Stokogard, Hollister Moisture Barrier, and Hydropel. In one study, the allergic reaction to plant resins was blunted more than 50 percent by the prophylactic use of these agents. Nevertheless, avoidance and the use of protective clothing remain the best forms of prevention.
When inadvertent contact with the plant is made, the skin should be cleansed thoroughly with soap and water or, better still, cleansed with plain rubbing alcohol to dissolve the resin. This is most effective when done within the first fifteen minutes after exposure, before skin binding by the resin is complete. After that time, a topical preparation such as Calamine lotion or Sarna lotion may be tried to promote drying of the lesions and to decrease itching. In many cases these simple measures will suffice.
More severe or widespread reactions frequently require the use of topical corticosteroid antiinflammatory agents, which are some of the most widely used preparations in dermatology today and the mainstays of dermatitis therapy. Depending on the severity of the condition, your doctor may prescribe a high-, medium- or low-potency variety in a lotion, gel, cream, or ointment formulation. In most cases topical corticosteroids are applied once or twice daily, and you can generally anticipate complete relief from the rash and itching within a few days. Topical steroids are usually discontinued once the symptoms have cleared, but some physicians may advise continuing them for a little while longer to reduce the small (but real) possibility of a rebound flare-up of the problem. Ultravate, Temovate, and Diprolene are brand-name examples of super-high-potency topical steroids, and Aclovate, Elocon, Locoid, and Hytone are examples of intermediate-and low-strength formulations.
Occasionally, poison ivy may be so severe that your doctor will prescribe an oral corticosteroid preparation such as prednisone or Decadron to bring your symptoms under control. These, too, in decreasing doses, may be continued for a week or two following the clearing of the symptoms to prevent relapse. Finally, when bacteria have invaded, a topical or oral antibiotic may also be prescribed to clear the infection and prevent its spread.
