By Richard P. Holm MD
His rash was itchy, raised, red, blistery, and distributed in streaks along both forearms. Likely this was from poison ivy, especially since he had been camping and hunting for firewood in a woody area that weekend. Although it was too early in the spring to see the groups-of-three glossy-pointed-leafed plants, he had been pulling on furry-rope-like woody vines, probably the winter-vine form of the poison plant. Allergists and dermatologists call the rash from poison ivy a form of contact dermatitis, which is an allergic reaction to the oil of the plant.
First exposure to the poisonous oil is the sensitizing dose and generally doesn’t cause a rash. The next exposure, however, brings on the allergic eruption. 85% of adults have been sensitized to poison ivy oil, sometime in the past.
Many other agents can also cause contact dermatitis, but rarely so violent as from oil of poison ivy. About 15% of us react to nickel, which is characterized by a dry scaly rash, hives, or blisters distributed on ear lobes, around necklaces, or under wrist watches.
Other allergic contact culprits include latex used in shoes, paint, and gloves; juice off of clams, oysters, and shrimp; perfumes blended with cosmetics, nail-polish, and skin-care-products; sticky adhesives used on tape, false-eyelashes, and toupees; and antibiotics found in Neosporin, Bactroban, and Triple Antibiotic ointments.
Some contact dermatitis is not allergy driven and happens because the agent is frankly toxic, like bleach, kerosene, battery acid, and cement. Also toxic, especially to those light-skinned, is excessive wetness, washing, and detergents. Another kind of contact dermatitis follows certain perfumes, insecticides and oil from the skin of a lime, but only when in combination with sun exposure.
Of course, treatment depends somewhat on the specific agent that causes the problem. Cleansing the allergen away might be important. Protecting with barrier creams and ointments like zinc oxide or CeraVe might help. Sometimes oral, not topical, antihistamines help, like Zyrtec or Allegra tablets daily, but not Benadryl lotion. Often topical steroids, like cortisone or triamcinolone cream, can help turn off inflammation. And when the reaction is severe enough, a tablet or injectable form of steroid may be prescribed by your doctor.
The most important lesson should be avoiding the allergic or toxic agent in the first place. My poison ivy patient was careful when he was in the woods from that day forward, especially when encountering furry-rope-like woody vines.