The brown recluse's venom is a cytotoxin that attacks the cells of flesh and produces necrosis, or dead tissue, in humans. Though fatalities from the venom are very rare, the reaction to the venom depends on the amount of an individual's sensitivity to the toxin. The bite is not usually felt, but a stinging sensation may develop, followed by intense pain. This reaction, however, may not occur until an hour or more after the bite. The bitten area will first develop a small, white blister and enlarge to the size of a silver dollar as the venom attacks and kills the tissue in the affected area. If bitten, call a physician or go to the emergency room immediately. Although no antitoxin is available, prompt medical treatment can prevent severe reaction and minimize the extent of damaged tissue and eventual scarring.