Poison Ivy, Oak and Sumac Rash: Itchy Blisters, Care and When to Be Seen

What it involves

MedlinePlus explains that poison ivy, oak, and sumac cause an allergic skin reaction called allergic contact dermatitis. The result is most often an itchy, red rash with bumps or blisters, brought on by the plants' oils, which enter the skin rapidly.

Who this is for

• Patients with a streaky, very itchy, blistering rash after time outdoors
• Patients whose rash is on the face, lips, eyes, or genitals
• Patients with a rash that is weeping, crusting, or getting more painful
• Parents of children who play in wooded areas and keep coming home with rashes

What to expect

• Questions about where you were, when the itching began, and whether you have reacted to the plants before
• A look at the pattern of the rash, since streaks and lines often point to plant contact
• A check for signs of infection such as pus or increasing tenderness
• A plan that may include creams, soothing steps, antihistamines, or a short course of steroid medicine for severe cases

Where the reaction comes from

MedlinePlus says the rash is caused by skin contact with the oils, or resin, of certain plants. Poison ivy grows as a vine with three shiny green leaves and a red stem and is found throughout much of the United States, while poison oak is mostly on the West Coast and poison sumac grows along the Mississippi River. The oils can linger on clothing, pets, tools, and shoes, so a second rash can follow contact with something that was not cleaned.

How the rash behaves

Symptoms MedlinePlus lists include:

• Extreme itching
• A red, streaky, patchy rash where the plant touched the skin
• Red bumps that may form large, weeping blisters

Timing and spread

MedlinePlus says the worst symptoms are often seen 4 to 7 days after contact and that the rash may last 1 to 3 weeks. It states that the rash does not spread by the fluid from the blisters, so once the oil is washed off the skin, it does not often pass from person to person. Smoke from burning these plants can cause the same reaction, and breathing it in may affect the throat and lungs.

First aid in the first half hour

MedlinePlus advises washing the skin thoroughly with soap and warm water as soon as possible, ideally within 30 minutes, scrubbing under the fingernails, and washing clothing and shoes in hot water. Animals that touched the plants should be bathed. Cool compresses, calamine lotion, hydrocortisone cream, and lukewarm oatmeal baths ease the itch. An oral antihistamine may help, and the itchy skin guide covers general itch relief.

When it needs more than home care

MedlinePlus says to contact a provider if the itching is severe and cannot be controlled, if the rash affects the face, lips, eyes, or genitals, or if it shows signs of infection such as pus, yellow fluid leaking from blisters, odor, or increased tenderness. In severe cases, particularly for a rash around the face or genitals, a provider may prescribe steroids by mouth or injection. A blistering rash that spreads in a sheet is different from the hives guide, and the shingles guide covers a blistering rash on one side of the body.

Emergency signs and prevention

MedlinePlus says to get emergency treatment right away for swelling or difficulty breathing, a past severe reaction, or exposure to the smoke of burning plants. To prevent a rash, it suggests long sleeves, long pants and socks in areas where the plants grow, a barrier lotion applied beforehand, learning to identify the plants, and removing them near the home, but never burning them. An outdoor rash may also be an insect problem, as the insect bites guide explains.

Sources

• MedlinePlus — Poison ivy, oak, sumac rash
• MedlinePlus — Poison Ivy, Oak, and Sumac