Urushiol (a ortho-diphenol with a long hydrocarbon chain) is an white/light yellow oil found mainly in the Rhus genus of plant life. The irritant in Poison Oak, Poison Ivy. Urushiol binds to the skin, and causes rashes to form in about 85% of all humans. Frequent exposure increases sensitivity.

Interestingly enough, Urushiol is also found in the shells of cashew nuts.

Urushiol oil is a toxic sap found in Sumac, Poison Oak and Poison Ivy and is what makes you break out in a rash when you come into contact with these plants. It is clearish yellowish sap and begins to darken when exposed to air and remains active(can cause a rash) for years after the plant it came from died. Because of this fact the Japanese would paint it onto gold objects to protect them from thieves, this is where it got the name, urushi, which is Japanese for lacquer. This fact makes Urushiol oil pretty useful for a whole bunch of nastiness because it stays active on basically everything. Jewelweed is a plant that contains lawsome which reduces the rash caused by the Urushiol.

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