Scientists estimate that about 85% of the population is allergic to the urushiol present in poison ivy, poison oak, and poison sumac. A very small amount of urushiol causes a rash — a billionth of a gram is enough to cause a reaction. However, the rash may take more days to present itself or not exhibit at all until after the first few exposures.
More about urushiol:
- The poison ivy plant belongs to the cashew family, called Anacardiaceae.
- Urushiol can stay active on a surface for up to 5 years.
- People who have a sensitivity to poison ivy also tend to be allergic to mango rind, which contains urushiol.