In North America, contact dermatitis from plant exposure is most commonly caused by poison ivy, oak, and sumac.
These plants secrete urushiol oil, which causes a type IV hypersensitivity reaction (cell-mediated, delayed) when in contact with the skin, GI tract, or respiratory tract (through smoke).
Patients often present days to weeks post-exposure, as the oil can stay on clothes, equipment, pets, etc. for up to years. As such, it is important to advise patients to thoroughly wash everything that may have been exposed ASAP. After exposure, it takes approximately 20-30 minutes for urushiol to penetrate the skin, so washing skin as soon as possible after a possible exposure can prevent reaction.
Rash is vesicular, pruritic, and linear. Appears 1-2 days post-exposure (possibly shorter if patient has prior exposure, longer if naïve).
The vesicles seen above contain clear fluid that is not contagious. Patients may say the rash is “spreading,” but they likely have just not fully decontaminated and still transferring oil to other parts of their body.
Treatment is generally supportive. Symptoms can be treated with oral antihistamines, calamine lotion, oatmeal baths, cool compresses, topical astringents under occlusion dressings to dry weeping lesions.
For severe reactions, 15-20 day steroid taper can be prescribed. Low-dose steroid bursts are not recommended, as rebound dermatitis is seen.
Not indicated are topical antihistamines, anesthetics containing benzocaine, antibiotics containing neomycin or bacitracin.