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Poison ivy, oak, and sumac: When does the rash appear?

The amount of time it takes for a rash to appear depends on whether you’ve had a rash from one of the plants before. Here’s the general rule:

  • Previous rash from poison ivy, oak, or sumac: A rash usually appears within 4 to 48 hours.

  • Never had a rash from poison ivy, oak, or sumac: It typically takes 2 to 3 weeks.

How do you get a rash from poison ivy, oak, or sumac?

Every part of these plants — the leaves, stem, vines, flowers, and roots — contains an oil called urushiol (yur-oo-shee-aal). When this oil touches your skin, it can cause an allergic reaction. Anyone who develops an allergic reaction gets a rash.

It’s easy to get this oil on your skin. This can happen when you:

  • Brush up against one of these plants.

  • Touch something that has the oil on it, such as your clothing, pet’s fur, or gardening tools.

  • Get tiny pieces of these plants on your skin or clothing when someone in the area mows or whacks at these plants to get rid of them.

Use caution while doing yard work

If you mow, whack, or burn one of the plants, you can cause a serious, life-threatening allergic reaction.

man cutting weeds

Why is it so dangerous to mow or whack at poison ivy, oak, or sumac?

When you use a lawnmower or trimmer to get rid of these plants, you break the plants into thousands of tiny pieces, which become airborne. If several tiny pieces land on you or someone else, many rashes can develop. This can cause a serious allergic reaction.

Is it safe to burn poison ivy, oak, or sumac to get rid of it?

No. When you burn these plants, their toxic oil gets into the air. The airborne particles can:

  • Land on anyone’s skin, including yours, and lead to a rash.

  • Cause a serious (or life-threatening) reaction when you and anyone else in the area breathes in the toxic smoke.

How can I tell if poison ivy, oak, or sumac caused my rash?

You won’t notice the oil on your skin; however, most people recognize the rash if they’ve had it before.

You want to see a medical doctor if you:

  • Are unsure what caused your rash

  • Never had a rash from one of these poisonous plants

It’s important to know what caused the rash, as many things can cause a rash.

If you’re certain that poison ivy, oak, or sumac caused your rash, here’s what you can do to treat it.

Poison ivy, oak, and sumac: How to treat the rash

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Centers for Disease Control and Prevention. “Poisonous plants.” Last reviewed 8/7/2018. Last accessed 7/23/2019.

McGovern TW. “Dermatoses due to plants.” In: Bolognia JL, et al. Dermatology. (second edition). Mosby Elsevier, Spain, 2008: 255-6.

Vaught CK, Mold JW. “Poison ivy: How effective are available treatments?” J Fam Pract. 2016 Nov;65(11):801-9.