Some people think they are immune to poison ivy
because they have never had a rash. However, it is possible to
eventually break out into a rash after being exposed to poison ivy
or oak enough times.
You can begin getting a rash at any time during your life. Like
other topical allergies, sensitivity is just a matter of being
exposed enough times until the body has an allergic reaction to the
rash-causing oil, urushiol. Since three out of four people are
sensitive to urushiol, it is only a matter of enough exposure
before most people react to the plants.
Sensitivity may also increase over time. With repeated exposure
to the plants, you may find the rash is more severe. Once you know
you are sensitive to urushiol, it is important to remove the oil as
quickly as possible when you know you have been in contact with
poison ivy or oak.