From early spring to late fall, your wilderness adventure can bring you into contact with poisonous plants. Whether it's poison ivy east of the Rockies, poison oak west of the Rockies, or poison sumac in the humid wet areas of the southeast, plants across the country are just waiting to give you a rash.
The first step in prevention is learning to recognize the plants. Poison ivy is a low-growing plant, a vine, or a shrub. The leaves can be either smooth-edged or notch-edged, and they're usually in groups of three. Poison oak is nearly always a small bush, but can also be a vine. Its smooth-edged leaves can be in groups of three, five or seven. Poison sumac is either a small tree or shrub. It's pretty leaves have nine to thirteen leaflets on a red stem, and flowers that become small white fruit. All of them irritate the skin.
Since it's hard to recognize them, and since their foliage is usually combined with other concealing foliage, the second preventive step is to dress for avoidance, although this may be uncomfortable in warm temperatures. A long-sleeved shirt, long pants (these are convertibles), high-cut boots, and long socks can help protect your body, but only gloves can save your hands.
These plants produce a oil or resin called urushiol that causes an allergic reaction when it touches the skin of about half the population. The oil can stick to your clothing, your pack, and even your pets and you can get the rash from touching anything that still has the oil. When you get home, thoroughly wash everything.
If you think you touched it, wash your hands immediately, using soap. The rash usually takes between 24 to 72 hours to develop, but for the 15% of the allergic population who are severely allergic, it can start as soon as 4 to 12 hours. In this case, urgent medical care is necessary, as it can become anaphylactic shock.
If you get the rash, you can treat it with oral antihistamines, which you should carry in your first aid kit, calamine lotion, and/or an antihistamine cream or cortisone cream. A cool damp compress helps soothe the rash, which generally goes away on its own in two to three weeks. If the rash is very severe, see a doctor for a prescription steroid, and take it long enough to completely cure the rash.
(Sources: http://www.medicinenet.com/script/main/art.asp?articlekey=82545 , http://www.duke.edu/~cwcook/trees/tove.html, http://www.emedicinehealth.com/allergy_poison_ivy_oak_and_sumac/article_em.htm )
