Poison ivy is a plant that can be found throughout the United States. It’s often found in wooded areas.

Along with plants like poison oak and poison sumac, poison ivy contains an oily sap that’s called urushiol.

Skin contact with urushiol can lead to an allergic reaction characterized by a red, itchy rash that may sometimes include blisters.

The reaction to urushiol is a form of allergic reaction called contact dermatitis. Anyone can potentially have a reaction to urushiol. But some may be more sensitive or tolerant to it than others.

You’re not born with urushiol sensitivity. But you can become sensitized to it over time.

When you’re first exposed to urushiol, your body usually signals your immune system to recognize it as an irritant. Your immune system then starts preparing a response to urushiol, should you be exposed again.

When you’re exposed again, your immune system may use this response, which causes the characteristic itchy red rash to occur. This is why some people appear to be immune to urushiol when they first encounter poison ivy.

There have been anecdotal reports of people consuming or working with poison ivy plants in order to build up tolerance to urushiol. However, there’s little clinical evidence to support that you can desensitize yourself to it.

Allergy shots can help decrease sensitivity in people with certain allergies. This is done by giving shots containing increasing amounts of a specific allergen, with the goal of building immunity.

There are currently no allergy shots available for urushiol, but one may be on the horizon.

Scientists are studying the body’s reaction to urushiol. In 2016, experts identified the immune protein that causes itching in response to urushiol. Blocking this protein decreased itching in a mouse model, though larger studies involving humans are still needed.

Sensitivity to urushiol can increase or decrease throughout your lifetime.

Remember, everyone has the potential to react to urushiol. While some people are less sensitive to it than others, increased exposures can eventually cause them to have a reaction.

You may also find that your sensitivity decreases over time. This may be due to the weakening of the immune system as we age, but research doesn’t draw any firm conclusions.

Is it possible for urushiol to enter your bloodstream and cause a systemic infection? The short answer is no. It’s important to remember that the reaction to poison ivy isn’t an infection. It’s a local allergic reaction.

However, sometimes the rash does appear to spread to other areas of the body. This can be explained in a couple of ways:

  • If you have urushiol on your hands or under your fingernails, you can spread it to other areas of your body through touch. Even if you’ve washed your hands after initial exposure, you can still re-expose yourself by touching clothes or tools that may still have urushiol on them.
  • It may take the rash longer to appear on some areas of the body. For example, the soles of your feet naturally have thicker skin, so a reaction there might develop later than one in an area with thinner skin, such as your wrist.

One way that urushiol can enter the body is through inhalation. This can happen if poison ivy plants are burned and you inhale the smoke. Inhaling urushiol can irritate the nasal passages and lungs, potentially causing serious breathing difficulties.

There’s no evidence that urushiol can lie dormant within your body and reactivate later. There are some viral infections, such as herpes simplex, that can do this, but remember: The poison ivy reaction is an allergic response, not an infection.

That said, while the characteristic poison ivy rash often develops in a matter of days, in some cases it can take up to two weeks to appear. This may make it appear as if urushiol lies dormant after exposure, but that’s not the case.

Urushiol is the component of poison ivy that causes an itchy, red rash to appear.

Anyone can develop a sensitivity to urushiol during their lifetime, and this sensitivity may change over time. But there’s no way for someone to be completely immune to the effects of urushiol.