Definition & Overview

Poison ivy and poison oak are two plants commonly known to cause a skin rash characterized by red, itchy, stinging irritation on the skin. Poison ivy can be a rope-like vine or a shrub, depending on where it grows in the US. It usually produces green or yellow flowers, white to green-yellow berries and has shiny green (or orange-red in the fall) leaves. What is easily distinguishable with poison ivy is that its leaves each have three leaflets.

Poison oak is similar to poison ivy such that it can either be a shrub or a vine, has leaves of three, and can cause the same type of skin irritation. However, it has a tendency to blend with its environment so it can be tricky to spot. It is known to grow mostly in the West Coast.

Cause of Condition

What do these plants have in common to cause such a similar rash to begin with? The answer lies in their oily sap called urushiol that is present in their leaves, stems and roots – even if the plants are already dead. Touching any part of poison ivy or poison oak can cause an allergic reaction. Even more worrisome is that touching other items that have come in contact with poison ivy or poison oak can carry the urushiol and can also trigger an allergic reaction.

But initial contact with the urushiol does not instantly trigger an allergic reaction. The allergen is initially absorbed into the skin, which then triggers the body’s self-defense mechanism to develop immunity against the allergen. That is why the first contact yields no symptoms. The next time that contact takes place, that is when the body goes into overdrive to defend itself leading to an allergic reaction such as a skin rash or dermatitis.

Urushiol from poison ivy and poison oak is not just dangerous when it comes into contact with skin. It is also dangerous when inhaled, when the plants are burned in an effort to remove them from the area. It can affect the throat, the nasal passages and lungs and may lead to a more severe allergic reaction.

Key Symptoms

Skin rash from poison ivy or poison oak is fairly common and three out of four people are found to be sensitive to the allergen. Symptoms usually appear within 24 to 48 hours after contact and may continue to develop up to six days after exposure. Redness and itching of skin are the primary symptoms. The redness gives way to rashes or hives that appear as streaks or patches on the areas of the skin that have had direct contact with the plants. The itching also becomes more intolerable.

As the skin irritation progresses, bumps or blisters develop from the rashes. These blisters can sometimes ooze liquid but will dry up and form a crust in a few days. The more often one is exposed to poison ivy or poison oak, the higher the chances that the symptoms will worsen and a more severe allergic reaction is to be expected. This may lead to serious symptoms such as:

  • Difficulty breathing or trouble swallowing
  • Eye or facial swelling
  • Rash that covers 25% of the body
  • Signs of infection from the blisters
  • Fever
  • Headache and nausea
  • Swollen lymph nodes

Who to See & Types of Treatments Available

Ordinarily, exposure to poison ivy and poison oak can be dealt with easily with home remedies. For instance, if there is a suspicion of poison ivy or poison oak contact, washing every part of the body that has come into contact with the urushiol is imperative. Clothing, tools and other equipment that may have also been exposed need to be immediately washed. If not, there is a possibility of transferring the said oils to other fabric and materials and the allergen will simply continue to spread.

Itching can be uncomfortable but one must, as much as possible, refrain from scratching. Taking cool showers may provide relief from itching. If necessary, calamine or hydrocortisone lotions may be applied to the rashes to temporarily stop the itchy feeling.

If the symptoms don’t improve and show signs of getting worse within 10 days, consult a dermatologist.


  • Shofner JD, Kimball AB. Plant-Induced Dermatitis. In: Auerbach PS, ed. Wilderness Medicine. 6th ed. Philadelphia, Pa: Mosby Elsevier; 2011:chap 63.
  • Smolinske SC, Daubert GP, Spoerke DG. Poisonous plants. In: Shannon MW, Borron SW, Burns MJ, eds. Haddad and Winchester's Clinical Management of Poisoning and Drug Overdose. 4th ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 24.
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