The rash will only occur where urushiol has touched the skin; it doesn't spread throughout the body. However, the rash may seem to spread if it appears over time instead of all at once. This is either because the urushiol is absorbed at different rates in different parts of the body or because of repeated exposure to contaminated objects or urushiol trapped under the fingernails.

The rash, blisters and itch normally disappear in 14 to 20 days without any treatment. But few can handle the itch without some relief. For mild cases, wet compresses or soaking in cool water may be effective. Oral antihistamines can also relieve itching.

There are a number of OTC products to help dry up the oozing blisters, including:

• aluminum acetate (Burrows solution)
• baking soda
• Aveeno (oatmeal bath)
• aluminum hydroxide gel
• calamine
• kaolin
• zinc acetate
• zinc carbonate
• zinc oxide

How to identify poison ivy, poison oak, and poison sumac

Unfortunately, poison ivy, oak and sumac don't grow with little picture ID badges around their stems, so you have to know what to look for. To avoid these plants and their itchy consequences, here's what to look for.

Poison Ivy

• grows around lakes and streams in the Midwest and the East
• woody, ropelike vine, a trailing shrub on the ground, or a free-standing shrub
• normally three leaflets (groups of leaves all on the same small stem coming off the larger main stem), but may vary from groups of three to nine
• leaves are green in the summer and red in the fall
• yellow or green flowers and white berries

Poison Oak

• eastern (from New Jersey to Texas) grows as a low shrub; western (along the Pacific coast) grows to 6-foot-tall clumps or vines up to 30 feet long
• oak-like leaves, usually in clusters of three
• clusters of yellow berries

Poison Sumac

• grows in boggy areas, especially in the Southeast
• rangy shrub up to 15 feet tall
• seven to 13 smooth-edged leaflets
• glossy pale yellow or cream-colored berries

Source: Food and Drug Administration