(Cercarial Dermatitis; Duck Fleas; Duck Itch; Duckworms; Sea Lice; Clam Digger's Itch)
by Cynthia M. Johnson, MA
Swimmer’s itch is a skin rash that appears on parts of the body that have been in natural bodies of water that contain certain parasites. It is more common in warm freshwater (lakes and ponds), but it can also occur in salt water.
This problem is caused by an allergic reaction to certain parasites. The parasite enters the water through the waste of infected birds and snails. It can burrow under the skin and cause a reaction when it comes in contact with a person's skin.
This problem is more common in children. This is because they spend more time in shallow water.
Other things that may raise the risk are:
Symptoms can start quickly. Problems may be:
The doctor will ask about your symptoms and health history. You will be asked about any recent time spent in natural bodies of water. A physical exam will be done. It will focus on your skin. This is enough to make the diagnosis.
The rash will go away on its own within a few days or up to one week.
Supportive care can help ease symptoms. Choices are:
People who are not helped by these methods may need prescription medicines.
The risk of this problem may be lowered by:
American Academy of Dermatology
Centers for Disease Control and Prevention
Canadian Dermatology Association
Public Health Agency of Canada
Colley DG, Bustinduy AL, et al. Human schistosomiasis. Lancet. 2014 Jun 28;383(9936):2253-2264.
Parasites—Cercarial dermatitis (also known as swimmer’s itch). Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/parasites/swimmersitch/index.html. Accessed March 19, 2021.
Schistosomiasis. EBSCO DynaMed website. Available at: https://www.dynamed.com/condition/schistosomiasis. Accessed March 19, 2021.
Swimmer’s itch. American Osteopathic College of Dermatology website. Available at:
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Accessed March 19, 2021.
Swimmer’s itch. DermNet New Zealand website. Available at: https://www.dermnetnz.org/topics/swimmers-itch. Accessed March 19, 2021.
Last reviewed December 2020 by EBSCO Medical Review Board Daniel A. Ostrovsky, MD
Last Updated: 3/19/2021
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