Poison Ivy FYI:
1. Poison Ivy does not cause an allergic reaction.
2. Poison Ivy NEVER "spreads."
Poison Ivy reactions are a chemical burn, not an allergy per se. You see the little blisters on your skin and they are chemical burns. The chemical is not under the skin to magically be released when you scratch or pop the blister. So called, spreading, can be caused by insufficiently cleaning the exposed area or by having the chemical under your nails, or clothing, etc.
Some people will swear that they had one exposure and that there was some early blistering and then some later blistering therefore, it spread. No, it didn't unless you didn't wash. Sometimes some areas of skin are more reactive to the burn. Its the same as a physical burn. The bottoms of your feet won't burn from a brief encounter with an ember for instance as opposed to your belly or your forearm.
I hate Poison Ivy and react to it every summer. Peed one time without knowing it was on my hands. Pretty impressive but not functionally useful.
Dutch