What Is a Poison Ivy Rash?

CDC's National Institute for Occupational Safety and Health says poison ivy, poison oak and poison sumac release an oil called urushiol when part of the plant is damaged or burned, and that most people who get the oil on their skin have an allergic reaction called contact dermatitis. The FDA says itching comes first, then a red rash and then blisters, which can appear anywhere from a few hours to several days after exposure to the plant oil.

It does not spread from person to person. The FDA says poison plant rashes cannot be passed between people, but you can pick up the rash from plant oil stuck to clothing, pets, garden tools and other items that touched the plants. It says the rash occurs only where the oil touched the skin, so scratching cannot spread it on the body, and a rash that seems to spread is either oil absorbing at different rates on different parts of the body or repeated contact with contaminated objects or oil trapped under the fingernails. Even if blisters break, the fluid is not plant oil and cannot spread the rash.

The FDA advises washing your skin with soap and cool water as soon as possible after contact, since the sooner you cleanse the skin, the greater the chance of removing the oil or helping prevent further spread. NIOSH advises wearing long sleeves, long pants, boots and gloves, washing exposed clothing separately in hot water with detergent, and never burning plants that may be poison ivy, poison oak or poison sumac, because inhaling the smoke can cause severe allergic respiratory problems.

For relief, NIOSH advises wet compresses, calamine lotion or hydrocortisone cream to reduce itching and blistering, and getting medical help in severe cases or if the rash is on the face or genitals. The FDA says not to scratch the blisters, because bacteria from under the fingernails can get into them and cause an infection, and that the rash, blisters and itch normally disappear in several weeks without any treatment.