Poison Ivy Rashes: The Facts

What causes a poison ivy rash?

The poison ivy rash (also called poison ivy dermatitis) happens after exposure to a poisonous plant. The rash is caused by a chemical in the plant oil called urushiol. Urushiol is found in poison ivy, poison oak and poison sumac. Urushiol causes an allergic reaction in the body. A person only needs to touch this chemical once to develop a reaction. Most people who get a poison ivy rash can remember being around poison ivy or have been in a grassy or wooded area recently.

What does the plant look like?

You may have heard the old saying, “leaves of three, let them be.” People use this rhyme to help them remember what poison ivy looks like and to stay away from it. It is true that poison ivy and poison oak plants usually have three leaves at the end of each stem. But, other plants containing urushiol sometimes have 5, 6 or even 7 leaves that are angled toward the top of the stem. In the fall, some of these plants produce “fruit” which looks white or green. Here are some pictures of what urushiol plants look like. Some even have black spots on the leaves.

Poison Ivy

Poison Ivy

Poison Sumac

Poison Sumac


Is there any way to prevent it?

The best way to prevent a poison ivy rash is to stay away from the plants! If you know you’ll be around the urushiol plants, wearing long sleeved shirts, pants, boots and hats is advised. The oil can go through rubber and latex, so vinyl gloves are recommended. Clothing helps to create a barrier between the plant and the skin but the oil can stay on the clothing or shoes for many days and if touched can be spread to the skin. Be careful removing clothes and wash in them warm water with soap immediately. There are barrier creams on the market which claim to prevent poison ivy but they are not 100% effective.

What can I do if I know I’ve been exposed to it? Is it too late?

If you know poisonous plants touched your skin, wash the area as soon as possible. If you’re able to get the skin clean within 10 minutes you can remove as much as half of the poisonous oil. One study showed that after the oil has been on the skin for more than ten minutes, removal is difficult. However, washing the area even two hours after exposure can decrease the severity of the rash. Be sure to clean under and around fingernails well. The rash develops within 4-96 hours of touching the plant.

 Once I have a poison ivy rash, am I contagious to other people?

Once poison ivy rash appears you are not contagious, even if there is fluid coming from the spots. The rash shows up first in one area of the body. Then it shows up in another area. When this happens people think the rash is spreading. Actually, once the oil is on the skin it gets absorbed into the body. In the body it can be carried to any location in the skin.  New areas appear because the poison is already in the body, not because it’s been spread from touching another infected area. New lesions can appear after the first rash and can even keep appearing 21 days after exposure to the plant!

Remember, oil can stay on clothes, shoes, gardening tools and pet fur for days and still be harmful. Make sure to decontaminate these objects if you suspect poisonous oil is on them.

What’s the treatment for a poison ivy rash?

The severity of the rash determines how it’s treated. For most people, the worst symptom is the itching. For usual cases Benadryl works, but some cases might require a prescription strength antihistamine. Itching can also be treated with oatmeal baths or wet compresses. Early in the course of the rash, topical steroids may be helpful. After the rash develops into fluid-filled bumps topical steroids don’t seem to help. Some patients report calamine lotion is helpful in reducing itching. In severe cases, your provider may prescribe an oral steroid.