The rash can affect almost any part of your body, especially where your skin is thin, such as on your face. A rash develops less often on the soles of your feet and palms of your hands, where the skin is thicker. The rash does not spread, although it may seem to when it breaks out in new areas. This may happen because urushiol absorbs more slowly into skin that is thicker, such as on your forearms, legs and trunk. We are not born with a sensitivity to poison ivy.
Sensitivity develops after the first direct skin contact with the oil urushiol.
An allergic reaction seldom occurs on the first exposure. A second encounter can produce a reaction, which may be severe. About 85 percent of all people will develop an allergic reaction when adequately exposed to poison ivy. This sensitivity varies from person to person. People who reach adulthood without becoming sensitive have only a 50 percent chance of developing an allergy to poison ivy.