First of all, you can transfer urushiol from one skin part to another. However, only in the first 30 minutes after contact, and the only times it has been reported are from hands to genitalia. Thus, wash your hands before going to the bathroom.
This is a review paper from 2006 that discusses the plants responsible for, the clinical manifestations, treatment, and prophylaxis of allergic dermatitis due to urushiol. We know them as poison ivy, poison oak, and poison sumac. They are all native to North America, and cause more than 7 million healthcare encounters per year.
Interestingly, the plant only secretes urushiol when damaged, so simply brushing undamaged leaves doesn’t cause dermatitis. However, bushwhacking, yardwork, and vigorous contact (don’t use them to wipe!) can. The causative agent is present in the leaves, stems, and vines, so absence of leaves in winter doesn’t mean it is safe to interact with the plant. The oil can be transferred to clothing and still cause dermatitis after drying. It cannot, however, be transferred by the dermatitis itself, and urushiol is nearly completely absorbed by the skin within 30 minutes of contact.
The dermatitis is a typical T cell mediated delayed hypersensitivity reaction. Sensitization does occur, so future contact is typically worse. Untreated, symptoms can last from 3-6 weeks. Occasionally “black spot dermatitis” occurs, where there is a dark spot on the skin that cannot be removed, and then dermatitis erupts later. Burning the plants does aerosolize urushiol, and the smoke can cause significant respiratory tract problems, as well as generalized dermatitis.
Treatment is best directed at stopping the immune response. If able to do so, wash the skin before the oil is absorbed. Several commercial agents are available, but none appear significantly better than soap and water. If unable to remove it before dermatitis occurs, the next line of treatment is symptomatic treatment with oral antihistamines, cool compresses, and possibly oatmeal baths. Topical antihistamines should be avoided. Moderate strength topical steroids (0.1% triamcinolone or betamethasone) can be used, but beware of thin skin or on children. Systemic steroids are better tolerated, but beware of rebound if treatment is inadequate.
Prevention is easier. Avoid the plant. If you have to go into environments where the plant is present, wear protective clothing. Be aware that urushiol can be absorbed through thin, sweaty clothing. There are commercially available barrier creams that are effective in small trials, and may be beneficial to people who have severe sensitization. Comically, the author reports that attempts at desensitization by eating the plant is ineffective, and causes pruritis ani.
Overall it’s a well written review article that isn’t out of date yet.
Gladman AC. Toxicodendron dermatitis: poison ivy, oak, and sumac. Wilderness Environ Med. 2006 Summer;17(2):120-8. [PMID 16805148]
EBM Gone Wild