Poison ivy like its buddies poison oak and poison sumac has an oil called guru shil when this oil touches your skin, tiny chemicals creep in, they’re really small if your body probably wouldn’t think much of them but they bind to skin proteins, an inquiring cell with octopus arms called Langerhans or antigen presenting cells APC grabs the protein with the poison ivy chemical because now it thinks the body is being invaded by a foreign substance so it needs to send a signal, the APC rushes from the skin to organs called lymph nodes to sound the alarm of a pending invasion, there they meet up with t-cells who are ready to help and expand into an army that’s prepared to meet a poison ivy, Jerusha invasion, these t-cells move back to the skin to wash for yerushalayim but even these people may eventually develop the allergy if you’re allergic. However the next time your t-cells see the signal again, they react by sprinkling out proteins called cytokines and chemokines, some of which reach your bloodstream. This causes a cascade of events leading to edginess and swelling, they also recruit cells called phagocytes such as neutrophils and macrophages that eat up and remove debris cell assassins called cytotoxic t-lymphocytes and natural killer cells and more helper and memory t-cells, all of these cells send more signals that draw more cells, the overall effect is like a faucet being turned on high. The killers destroy the Arusha bound tissue but collateral damage occurs and healthy cells can also be killed, your skin turns red and blisters fill with fluid as the deluge of cell killers continues your reaction will depend on how susceptible you are to you. How much oil has gotten into yours? how much you’ve been exposed to poison ivy in the past? the chain of events is complex and it takes time, in fact it could be 48 hours before you develop an itchy rash and blisters, if exposed you can minimize your allergic reaction by scrubbing your skin with soap and water as soon as possible because it’s an oil Jerusha you get on your clothes, tools or pets and can touch your skin later with the same nasty effect so carefully wash those too of course, the best thing is to avoid poison ivy oak or sumac in the first place.