Swimmer’s itch is an allergic reaction to a small parasite called a blood fluke.
These tiny parasites are released from infected snails into fresh and salt water
such as lakes, ponds, and ocean bays. Normally, the blood flukes infect a bird
or mammal by burrowing into these animals’ skin. Sometimes the blood flukes may
burrow into the skin of people wading, playing, or swimming in infested shallow
waters. After entering the skin of people, the flukes die, causing an allergic
reaction that results in intense itching, a rash, and sometimes small blisters.