What Percentage of People Are Sensitive to Poison Ivy?

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.