What exactly causes poison ivy and oak blisters?


The blisters are the body's natural allergic reaction to contact with the poisonous plants.  The blisters do not cause the rash to spread.  You should never break the blisters.  An open blister can easily become infected and lead to blood poisoning.  If the blisters break, cover loosely with a sterile bandage.   In severe cases contact your doctor.