Poison oak rash is an allergic reaction to the leaves or stems of the western poison oak plant (Toxicodendron diversilobum). The plant looks like a leafy shrub and can grow up to six feet tall. In shady areas, the plant can grow like a climbing vine. The leaves usually have 3 separate leaflets, but there can be up to 9 leaflets, each about 1 to 4 inches long.
In spring, the leaves can be red or green. The plant produces small flowers that are white, yellow, or green. During the summer, the leaves are green and the plant grows berries. In late summer, the leaves turn red and orange.
Like poison ivy and poison sumac, poison oak releases an oil called urushiol when damaged. The allergen is absorbed into your skin when you touch the plant.
According to the University of California Agriculture & Natural Resources, only about 15 to 20 percent of people aren’t allergic to poison oak. The best way to prevent poison oak rash is to learn to recognize the plant and avoid contact with it.
If you’re allergic to poison oak, signs will begin to appear 1 to 6 days after exposure. Most of the time, you’ll notice it within the first 24 to 48 hours.
The most obvious evidence of an allergic reaction is skin rash, also called dermatitis. First, you may notice some stinging, itching, and minor skin irritation. Eventually, a red rash breaks out that gets itchier as it progresses. The rash will be worse in the areas that had direct contact with the plant. Bumps will start to form and eventually turn into large blisters that ooze liquid. Within a few days, the blisters begin to dry up and form a crust.
Poison oak rash is most likely to appear around your wrists, ankles, and neck, where the skin is thinner. The rash usually peaks about a week after exposure and lasts 5 to 12 days. In rare cases, it can last a month or more.
If you’re allergic to something, the reaction has the potential to be stronger each time you’re exposed to the allergen. Signs of a severe allergic reaction include:
- difficulty breathing
- trouble swallowing
- eye or facial swelling
- rash on your face, lips, eyes, or genitals
- rash that covers more than 25 percent of your body
- signs of infection, such as pus or yellow fluid leaking from blisters, or blisters that have an odor
- swollen lymph nodes
These symptoms can be life-threatening and require immediate medical attention.
Most of the time, poison oak rash can be treated at home. If you think you’ve been exposed, you should remove your clothing. Wash your clothes and anything else that may have come into contact with the poison. The oils from the plant can remain on fabric and other materials and can give you another rash.
Also wash your body well with plenty of lukewarm water and soap. Pay special attention to your hands, fingernails, and whatever skin may have touched the plant.
The rash can be very itchy and the temptation to scratch is strong, but scratching can cause an infection. Touching the blisters can also result in infection. Take lukewarm baths or cool showers to ease itching.
Over-the-counter remedies like calamine lotion or hydrocortisone cream may temporarily take care of the itch. You can also try applying cool compresses to the itchy patches. Antihistamine pills can also help with the itching. But be careful — antihistamine on your skin can make matters worse.
See your doctor or dermatologist if symptoms don’t improve within 10 days. A poison oak rash can be diagnosed by its appearance.
The oil can be contagious. You can have an allergic reaction by touching the plant, but also clothing or other objects that came into contact with the plant. The poison oak rash itself is not contagious. There’s no oil in the blister fluid, so you won’t spread it from one part of your body to another by touching or scratching (although you should avoid touching and scratching). The rash doesn’t spread from person to person.
Burning poison oak can disperse the oils in smoke, leading to severe respiratory problems and lung irritation. You should seek immediate medical attention if you’ve been exposed to burning poison oak smoke.