The Rhus group of plants, including poison ivy, poison oak, and poison sumac is probably responsible for more cases of allergic contact dermatitis than all other agents combined. These plants are extremely common in many areas, and about half of the popu­lation is allergic to them; another 20 percent would become so if casually exposed to the plants. The flowers and fruits of the Rhus group are white to yellow. The rash is caused by arloily substance, referred to as urushiol, excreted in the sap of the plants. Since the active agent is the same for all these plants, the rashes caused by them are indistinguishable. Dead plants, stems, twigs, roots, or particles of plant matter carried in smoke can produce wide­spread and severe dermatitis.

Common poison ivy is found throughout the United States and Canada, with the exception of the extreme southwest and the west coast. The plant grows as a vine or low-growing shrub without support; its leaves are arranged in groups of three and usually have notched edges.

Poison sumac is found as a shrub or tree, but never a vine, in damp, swampy areas, particularly in the eastern United States. The leaves are arranged in pairs along a central rib. The pairs number from seven to thirteen and have a single leaflet at the end.

Jingles helpful to remember:

Leaves of three, let it be;
Leaves of five, let it thrive!

Leaves of three, quickly flee;
Berries white, poisonous sight!

Fruits yellow, poison a fellow;
Fruits red, go ahead!

Those who are allergic to the Rhus plants may also be allergic to several related plants, including the mango, found in Hawaii, California, and Florida; the ginkgo tree, found in the southeastern United States; and cashew nut shell oil.


The early stages of contact dermatitis are best treated with cold, wet soaks or dressings, especially when there is blistering and oozing. These soaks cleanse and dry the area, regardless of the cause of the rash, and relieve itching and burning. Wet dressings may be applied by dipping a turkish towel or clean cloth in cool tap water or ice water. (A colder solution is more effective in relieving itching.) One can combine water and cracked ice, wrap it in a towel, and apply it directly to the area. Larger areas may be soaked in pans, buckets or tubs, but the water should not be ice cold. A bath tub is especially useful when the rash covers much of the body or involves the groin, buttocks, or genitals. (See the Formulary for a description of agents and methods for soaks and wet dressings.)

Calamine lotion is very helpful in the acute blistering and oozing stages of contact dermatitis. It has a drying effect and relieves itching. Several gels are also useful (see Formulary). Once the rash becomes dry, soaks and drying agents should be discon­tinued, since continued drying may be used for scaling, peeling or chapping.

Individuals with severe cases of contact dermatitis should see a physician. A doctor treating such a case will probably prescribe either antihistamines to be taken orally, or cortisone derivatives in spray, cream, oral or injection form.

At this point, I would like to condemn the use of some of the over-the-counter, non-prescription preparations used for the treat­ment of poison ivy and similar problems. Topical anesthetics, especially benzocaine, are notorious agents of allergic contact dermatitis. Antihistamines, though they seldom cause allergic reactions when given by mouth, may do so when applied to the skin. Zirconium compounds can also produce persistent skin reactions. In general, allergies to medications develop more readily when they are applied to the skin than when they are taken internally. Only the strongest of these medications contain enough benzocaine to relieve itching. Moreover, the only preparation that contains enough benzocaine to be effective when applied to the skin is an ointment intended for use on hemorrhoids! Like­wise, antihistamine creams and zirconium compounds are of ques­tionable effectiveness.

When purchasing medications for use on the skin, be sure to read the container label carefully. It should list each ingredient. The names of antihistamines generally end in -ine or -amine, as do a number of non-antihistamines. The names of medications related to benzocaine usually end in -caine. If there is any doubt as to whether a preparation contains an antihistamine or benzocaine, ask your pharmacist. Don't ask him whether you should use it or not-you already know! Just put it back on the shelf and look for something else. Remember, you can't go wrong with plain cala­mine, but Caladryl contains an antihistamine!


Any type of contact dermatitis, whether allergic or irritant in origin, is much easier to prevent than treat. Learning to recognize poison ivy is simple, but this cannot prevent unwitting exposure, e.g., to vines, roots, or smoke when the characteristic leaves are absent. Elimination of the plants and vines from yards, gar­dens, campgrounds, picnic grounds, parks, and other areas fre­quently visited is of clear value. Protective clothing should be worn. If it is feared that the clothing has been contaminated with the plants, it should be removed and laundered as soon as possible. Protective creams or ointments are used but generally have been disappointing.

If the skin has been exposed to a plant in the Rhus group, one should bathe as soon as possible. The oleoresin penetrates the skin very rapidly; in order to prevent the rash entirely, it must be washed off within ten minutes. The rash itself is not contagious, though any oleoresin remaining on the skin can cause more dermatitis in the same person or someone else. The fluid from blisters or oozing skin does not contain the oleoresin and cannot spread the rash, though it may irritate the skin.

Newer Post Older Post