Toxicodendron radicans, or poison ivy
, is a small plant with three leaves that secretes urushiol, which is an oily substance, on its leaves. It is the urushiol that actually results in the rash in the host. To understand the rash that results from poison ivy, you must first understand something about allergic responses. There are 4 different "types" of allergic responses in the human. The type 1 allergic response is the one that most people are familiar with as it is the immediate allergic response that is mediated by histamine. Poison ivy elicits a completely different response however, called a cell-mediated immune response, or type 4 immune response. This usually takes much longer to manifest itself than a "classic" allergic response, but also takes longer to go away. Initially with exposure to poison ivy, any contact with the affected skin may spread some of the oil causing the rash to other parts of your body...thus I wouldn't recommend putting any make-up on at this time as you wouldn't want to spread it. If you have had it for a few days, the oil is likely gone, so the risk of spreading the rash shouldn't be very high. However, sometimes cosmetic products themselves can cause a dermatologic reaction, especially when the skin is already irritated. And I would hate to make a bad rash worse, and not know if it was the poison ivy, or the make-up that was making it worse. For this reason I would probably stay away from it. If your rash doesn't seem to be going away after a couple weeks, or if it is very bad, I would recommend making an appointment to see a dermatologist
to get it looked at. Best of luck.