This is the most common causes of allergic contact dermatitis among both children and adults. When the leaves of these plants are broken or crushed, they release an oily substance that can provoke a significant allergic response in many (but not all) people. When this substance penetrates the skin, it stimulates the immune system to respond more vigorously to it in the future. The person is now sensitized to the plant, and the next time it touches his skin an intense, itchy inflammation of the skin (or dermatitis) erupts at the point of contact. This rash is an internal response of the allergic individual and is not contagious, however, if the oil from the plant is not washed from one person’s skin or clothing, it can be transferred accidentally to someone else through direct contact. This can give the misleading impression that plant dermatitis is contagious. Despite their dangerous sounding names, these plants do not contain any poisons or toxins that directly damage skin.
Reactions to one of these plants will vary from person to person and will depend on the size of the exposed area and the thickness of the skin involved. Thick skinned areas such as the palms and soles tend to suffer little reaction, while thin skinned areas such the forearm and face develop a rash more quickly and severely.
In the sensitized person, a skin rash will break out within a few hours of new contact with the plant. Itching is common and often intense, and blisters may form on the involved areas. There is often an oozing yellowish liquid, which can become crusted. Contact of the plant with eyelids or with male genitalia may provoke marked swelling in these areas. Areas exposed to less of the plant allergen may respond several days giving the misleading impression that the eruption is spreading. In the absence of complications or continued exposure, the eruption rarely lasts longer than several days.
Due to the fact that it takes about ten minutes for the plant allergen to penetrate the skin, rinsing the affected area with water immediately after exposure may prevent sensitization or an allergic response. Do not try soap which removes protective oils from the skin and may increase the allergen’s penetration.
Once the rash develops, nothing will reduce its effect. However, if the area of skin involved is relatively small, early application of a steroid cream can reduce the severity of the dermatitis. One percent hydrocortisone cream (nonprescription) may be used, or a strong preparation may be prescribed by a physician. If it is widespread, the doctor may prescribe oral steroids. When used as directed for several days, this medication can help calm an intense allergic response.
Cool, moist compresses and calamine lotion can reduce itching and irritation. Oral antihistamines such as Diphenhydramine (Benadryl) can reduce itching, and their sedative action may promote sleeping.