How does poison ivy rash spread?

So who (or, what) is the culprit behind the spread of poison ivy rash? A highly concentrated, invisible oil called, urushiol. Urushiol, is the rash-causing oil found in all parts of poison ivy, poison oak, and poison sumac plants. Approximately 85% of the population experiences an allergic reaction to these noxious plants, and according to the National Institute of Occupational Health & Safety, 50 micrograms of urushiol is enough to cause a rash in 80-90% of adults. That is less than one grain of table salt!


Contact with urushiol can happen in two ways. The first, direct contact with any part of the plant. Poison ivy plants and poison oak plants can be hard to identify as they can grow in several forms. These noxious plants have been known to grow as bushes, ground cover, and creeping vines. Often times, a person comes into contact with them, and doesn't even know it. The second way to come into contact with urushiol is through secondary contamination, or indirect contact. Urushiol can last on inanimate objects for a period of months, even years, as it does not evaporate. Therefore, the next time you come into contact with one of these items, you could possibly develop a rash.

Absorption Rate

In many cases, after coming into contact with urushiol oil and once the initial breakout has occurred, new spots will appear a day or two (or, more) later. This leads many to believe that the rash is "spreading." However, this may be due to absorption. Because some areas of the body have thicker skin than others, urushiol can be absorbed at a slower rate than areas of the body where the skin is thinner. Therefore, rashes in areas with thicker skin may not appear right away.

How Spreading Occurs

If the oil is not properly removed with a cleanser specifically designed for poison oak and poison ivy (such as Tecnu), urushiol can remain on the surface of the skin and continue to spread to other areas of the body. Typically, urushiol is absorbed within the first 8 hours after exposure, although this can vary. Surprising to many, the liquid that oozes from the blisters of a poison ivy rash does not spread the oil. By the time blisters form, your body has already absorbed the urushiol.


After coming into contact with these poison plants, showering rather than taking a bath is always recommended. As soothing as a nice, hot bath may sound, it can potentially make your rash worse. Upon submerging yourself in water, there is a chance that the urushiol on your skin can lift, and settle on top of the water, giving the urushiol a chance to spread to other areas of your body. Now, after the first shower using a cleanser such as Tecnu®, it is OK to follow up with a bath should you choose.

Hot water

It is never recommended to take a hot shower immediately after exposure to poison ivy or oak. The reason being, hot water opens yours pores. If urushiol is on the surface of the skin, and the pores open up, more urushiol stands a chance of being absorbed into your system. For that reason, showering with cool or lukewarm water for the first shower after exposure is best. With the initial shower, we recommend using a cleanser designed to remove urushiol such as Tecnu Original or Tecnu Extreme. Subsequent showers can be taken with hot water.