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Why Are Some People More Susceptible To Poison Ivy Than Others?

Poison Ivy Allergic


Why Are Some People More Susceptible To Poison Ivy Than Others?

Why is it that some people can lay in poison ivy for hours and nothing happens, yet others have severe reactions with the slightest exposure?

To find out, we’ll need to take a closer look at what causes the reaction.

The Cause

Poison ivy (as well as poison sumac and poison oak) contain an oil called Urushiol. This oil is what causes the allergic reaction associated with poison ivy. Urushiol has a dermatitis-producing principle, pentadecylacatechol. This chemical does not evaporate and will dry quickly on objects it comes into contact with.

This chemical can remain potent for a year or more. It is important to wash any objects, especially clothing after contact with poison ivy. The resin will remain active on these articles and can cause a rash months, or even years, later.

The word ‘urushiol’ is derived from ‘urushi’, The Japanese name for lacquer. The Japanese lacquer tree contains small amounts of urushiol in its sap, and those who are sensitive to the oil can even react when they come into contact with lacquered furniture from Japan.

So why are some people more sensitive than others?

Roughly 85% of all humans will acquire or have an allergy to poison ivy. The remaining 15% are completely immune, able to roll around in it without having a reaction.Poison Ivy There is no guarantee however, that a person who is resistant won’t become sensitive later on down the road. This is because people aren’t born with allergies; they develop them after exposure. Repeated exposures can make one even more sensitive to the irritant or allergen.

It is very uncommon for those under the age of five to get the itchy rash and blisters associated with a poison ivy reaction. Sensitivity for many can also fade with age, and quite a few adults who suffered severe reactions as children will find that they are no longer allergic or have a very mild reaction to poison ivy later in their life.

This means that the people who don’t seem allergic to poison ivy might lie in the 15 percent who are resistant, or they may just no longer be as sensitive as they were as a child.

Is there any way to prevent minimize exposure?

Aside from avoiding the plants entirely and using common sense, many forest service employees spray antiperspirant deodorant on thier exposed skin before they go out if they they think they might come in contact with poison ivy. The aluminum chlorohydrate may help prevent penetration of the oil through the skin.

If you do come into contact with poison ivy, the best preventive method to minimize exposure is to wash with lots of soap and water within 15 minutes of contact. After 15 minutes, the chemical that causes the reaction has already bonded to the proteins in your skin.

If a severe reaction develops, contact a dermatologist immediately, or go to an emergency room. Prescription medication may be needed to reduce itching and the swelling.

Hawley’s Condensed Chemical Dictionary, 14th Edition, 2002, John Wiley & Sons, Inc.
Donald G. Barceloux (2008). Medical Toxicology of Natural Substances: Foods, Fungi, Medicinal Herbs, Plants, and Venomous Animals. John Wiley and Sons. pp. 681
Robert Alan Lewis (1998). Lewis’ dictionary of toxicology. CRC Press. pp. 901



  1. J. Tippins

    October 2, 2012 at 8:58 am

    Be aware that poison ivy will attack you no matter what age. I am 82, and just recovering from one of the worst attacks of my long life. Note that the P. I. leaves are red, yellow, and orange during the fall, which is what attracted me because I was collecting fall leaves for an art project. Remember, to ID the poison ivy VINE, look for hairs on the stem.

  2. Luke

    July 8, 2013 at 2:50 pm

    This article actually doesn’t at all explain why the 15% aren’t affected. There’s some level of false advertising happening here.

    • Linda

      August 23, 2013 at 11:26 am

      I have yet to find anyone who discusses the ‘why’. Only the ‘how’ and ‘how many are effected’. Funny, ‘why’ is in the title, but isn’t really answered, unless you want to attribute it to increased exposure, but that doesn’t really explain it, IMO. I used to never be sensitive to poison ivy, then became so, then wasn’t again later. I attribute it to my immune system’s handling of stress, and this may be a key. Generally, as people age, their immune system takes more and more hits. Older people may lose sensitivity, as often the stress of performance decreases.

    • James

      May 25, 2014 at 8:38 pm

      I have always been one that couldn’t get it… It’s true that I haven’t “tested” my immunity lately but I lived near a deep wooded area which was laden w/ the stuff I’d play Army for hours in those woods and upon noticing that all of my friends would get it. I did seek these areas as hiding spots and never again never developed Poison ivy.

      I believe I have at least part of the answer; I have always had very, as in extremely, oily skin as a youngster and well into my 30s and it is my belief that the oil somehow “protected” me from the effects.

      • Arv

        September 14, 2016 at 1:29 pm

        I’m not allergic and don’t have oily skin. So while it’s still possible that your oily skin is part of the answer for you, it’s not a necessary condition for immunity.

  3. Steve

    July 27, 2014 at 12:05 pm

    My father used to brag about his immunity to poison ivy. He said he he would play in it barefoot as a child. He would pick leaves and rub them on his arm, and nothing. One day, when he was in his late 50’s, he was picking blackberries that were covered with poison ivy(bad idea because unless he washed them well, the toxin could gotten into the preserves my mother was making). THIS time, he got a reaction. I suppose that this one last time is what sent him over. I’ve 44 and have never had Poison Ivy but my ex-wife could get it by just being near the stuff. I’ve weed whacked poison ivy in shorts(by accident) and no response, but as rule, I avoid contact. The stuff is nasty, the oil can stay around for years. Say you use a hoe to hack a plant, then place in in your garage without washing, you don’t use the hoe for a year…. then pick it up, if you’re sensitive, you can still get a reaction. Also interesting is that it’s only Humans that appear affected. Your pets won’t get poison ivy, but they will get the oil on their fur, and you can get a reaction by petting them.

  4. Steve

    July 27, 2014 at 12:10 pm

    15% don’t have a response just like 15% HAVE a response to latex. To 20% of the population Cilantro tastes like soap. It’s genetic. The numbers aren’t exact of course, it’s a rough estimate. What’s unique is that reactions can work backwards with this stuff. You’re ‘immunity’ in weakened with each exposure. See the story about about my dad. You can actually build up a sensitivity over time. I won’t say I’m immune but I’m not as sensitive as some.

  5. Ted

    March 26, 2015 at 11:58 pm

    I have always been allergic to poison ivy. I get it from handling firewood and from my dogs.They dig in the woods which is full of poison ivy and the roots I know several times I got it from their paws. I’ve never had a mild case of it until the last few years. I looked and looked for something better than Calamine lotion. I thought something had to be better than that. I read that vinegar was good to wash the oil off. So far that has worked great. I’ve experienced it enough to know what that first little itch feels like before anything is visible. It has stopped it every time and I was surprised to learn it will even stop it after a rash begins. Before I started using vinegar it would get worse and worse and easily last a for weeks or a month. I have no doubt it has worked for me.

  6. Charles_Miller

    June 4, 2015 at 9:29 am

    Starting at the age of 15, I worked in a tree-cutting crew, and I quickly became “the golden child” when the rest of the crew discovered that I was immune to poison ivy, poison oak, and poison sumac. It thus became one of my tasks (a very important task) to go in and rip out all the toxic plants barehanded and dispose of them, clearing the way for the other guys to do their jobs. All of the other guys were allergic, but I never had so much as an itch from contact with any of these plants. Today I’m 55 years old, and I’m still ripping out poison ivy, poison oak and poison sumac around my property and for my neighbors, doing so barehanded with no reaction whatsoever. My old doctor explained to me once that about two-thirds of the human population of this planet are allergic to poison ivy and similar toxic plant oils, while my newest doctor claims that about 85% of all humans are allergic. Yes, there are some people who have less severe allergic reactions than others, but true “immunity” is NOT a myth. There are, indeed, a small number of people in the world who are completely and permanently immune to poison ivy, poison oak, and poison sumac.

    While natural immunity may sound desirable, it actually has some huge drawbacks; mainly, the fact that I can go hiking or rolling around in poison ivy with no reaction means that I’m not always AWARE that I’m carrying the toxins on my skin and clothing. Thereafter, everything I touch and everyone with whom I come in contact can become contaminated with the toxic oils. This generally means that (when I’m returning from the wilderness) I have to strip down and rinse myself with a concoction of water, liquid dish detergent and rubbing alcohol and throw my clothing in the back-porch washer BEFORE I ever enter the house or even touch the doorknob. Sometimes being immune isn’t as advantageous as it sounds at first.

    • Ben

      June 16, 2015 at 7:06 pm

      Anyone else in your family resistant? People often say it’s genetic, but if that were true you’d expect it to run in families.

  7. Mary

    September 6, 2016 at 12:41 am

    I am one of those people who are completely immune to poison oak, ivy, and sumac. The reason? I have O-negative blood. This blood type is very rare; it was said that 15% of all people in the world have Rh negative blood. However, only 6.6% have O-negative blood.
    I donate Anti-D plasma to make the Rhogam shot for pregnant women. There are also some of us that have two markers that make us immune to HIV/AIDS.

    Everyone that I have met that has O-negative blood is immune to poison ivy, oak and sumac. I have not met one that wasn’t, yet. Only 6.6% of the population has O-negative blood.
    I have never had an infection of any kind, never had stomach problems. Not even a tummy ache or heartburn. My eye site is 20-10 now; it used to be 20-5 and that always baffled the doctors, especially when doing my eye test at the DMV, and I would read all the lines including the company name that created the chart and ‘Made in Korea” at the bottom! I only recently learned that it is my blood type that is the cause. It is crazy. I just thought I was strange, but the more people I meet when donating Anti-D plasma, the more I know I am not alone.

    If you have this blood type, please donate blood and plasma. I make quite a bit of money donating Anti-D plasma. There are many clinical trials that are ongoing. They are testing the use of O negative blood for an HIV vaccine and other diseases/conditions.

    My daughter is also immune she has O negative blood.

    • Arv

      September 14, 2016 at 1:31 pm

      I’m not allergic and don’t have O-negative blood.

      Do you have any sources for your claims?

    • Pat

      October 7, 2016 at 1:52 am

      My husband is O negative, extremely allergic to poison ivy, sumac and oak, wears glasses and has IBS….so your theory isn’t too accurate. Like you, he gives plasma.
      I am O positive and have never had any allergies to these plants, neither do my parents, siblings, children and grandchildren.

    • Madeline

      June 30, 2017 at 5:35 pm

      Very interesting. I am O negative (didn’t realize it was rare) and I don’t get poison ivy either. I pulled it out for the last three weekend and my helper who pulled none of it but just dumped the weeds into the pile from a wheel barrel is covered in it. The O negative theory is worth research!


    October 14, 2016 at 9:56 am

    On the west coast we have Poison Oak, which is similar to Poison Ivy. I have been exposed to Poison Oak man many times over the years. The first time I was 14 years old and playing hide and seek with friends. One of those friends and I hid in a patch of Poison Oak. We hid for a long time and during that time (out of boredom) I chewed on some of the leaves. The next day, my friend called to see if I was blistered like her from our contact with Poison Oak. She was covered and I had no rash or blisters, at all. Over the years, all of my siblings, have had contact and all have suffered rashes and blisters. All of my children and grandchildren have responded the same way. I seem to continue to have no response, although I have terrible allergies to Oak tree pollen.

  9. Brett

    November 8, 2016 at 12:17 am

    This didn’t explain what it said it would…. I wanted to know why I get poison ivy constantly, all over my body, it looks like I have leprosy and itches so bad. I know what it looks like and make sure to never go near it, we don’t have it in our yard but stil, I even get it in the winter. Most people “get” it here in Oklahoma, but it’s a little rash. Not me. I wanted to know why our bodies reacted differently…

  10. Annette

    August 9, 2017 at 8:01 am

    I think whether you are allergic or not may be inherited. At least that’s all I can think of. My dad wasn’t allergic and neither was I. My brothers seem to get poison ivy if they went anywhere near it. And my sister has had poison sumac. I have heard that immunity can go away as you age and I haven’t been near it in ages and don’t plan on testing the theory just in case.

  11. Theresa

    April 14, 2019 at 7:25 am

    My spouse is very sensitive and I am immune. We have two children, one who is immune and one who is partially immune. She develops a few spots where as my husband has a full on rash. We were working in the yard and it is very interesting to see the varying levels of immunity to exposure.

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