Signs and Treatment of Swimmers Itch


First identified in Douglas Lake, in Michigan, USA, over 70 years ago, swimmers itch (also referred to as cercarial dermatitis, duck itch and schistosome cercarial dermatitis) is a common problem among those that enjoy natural waterways such as lakes, rivers and ponds .

The condition is caused by a parasite; small worms that bury themselves beneath the skin and die. The worms dies because birds and snails are natural hosts, while humans are not.

The swimmers itch is actually an allergic reaction to the worms. The rash and itch reaction, which happens within hours to days, is typically short-lived; usually about a week. Symptoms will appear in up to 2 days after being exposed. Swimming pools that are properly chlorinated do not spread this condition.

Most people do not show any allergic skin reaction when exposed to the protein that causes this condition, so it is possible to see no symptoms or different symptoms from person to person.

Swimmers Itch Rash on Leg - 219px x 254px - Example 1Swimmer's Itch on Leg


swimmers itch worm - Cercariae of Austrobilharzia variglandisSwimmers Itch Worm (Cercariae of Austrobilharzia variglandis)

The causes of swimmer’s itch are related to a variety of flatworm parasites, which belong to the Schistosomatidae family. These little critters use hosts, such as snails and birds, to complete their lifecycles, but at one point during their cycle, they leave one host to search for another. If you’re swimming and get in their way, they end up burrowing under your skin, where they die once you leave the water.

Their death causes your body’s immune system to respond by breaking out in a red and extremely itchy rash. While it may start out as a mild reaction, it typically escalates and the initial red “spots” become bumpy papules. Each bump is the graveyard of a flatworm that penetrated your skin after you were done swimming.


Swimmer's Itch Worm Lifecycle:

  1. Hosts of the worm that causes swimmer's itch, such as geese, ducks, shorebirds or seaguls have adult worms in the blood vessels. These worms spread eggs that are passed via the feces.
  2. When the eggs are exposed to water, they hatch and produce a ciliated miracidium (baby worm) that infects a snail (gastropod) as an intermediate host.
  3. The parasite develops in the snail to provide what are called "free swimming cercariae" which are worms that are released. These worms penetrate the skin of any nearby birds and move to the blood vessels.

When humans are present instead of snails, the worms will be attracted to the human skin and burrow in when the person leaves the lake as a means of survival during the water evaporation process.  Areas where water collects and gives the worms more time to burrow, such as leg openings or at the waist of a bathing suit are more susceptible to the "swimmer's itch."


The first signs that you may have swimmer’s itch will be a red rash that may or may not itch severely. Not all people react to swimmer’s itch in the same way and some may develop a mild irritation to a severe and horrendously itchy red rash. If you do scratch it too much, you run the risk of infection.

The degree of your symptoms will largely depend on how many of the worm larvae you get on your skin and how sensitive you happen to be to them. The more you are in contaminated water, the worse your symptoms may be. Typically, symptoms also get worse with repeated exposure.

Swimmer's Itch on Upper Leg - 352px x 253px - example 2Swimmer's Itch on Upper Leg or Thigh

You will start itching virtually the moment you dry off after getting out of the water, as that is when the larvae is burrowing into your skin. You may feel an odd tingly, burning sensation as the larvae start to get under your skin and it may start immediately. Shortly afterwards, you may also see small red dots that will blossom into a larger red rash as time passes. The initial tingle will typically be replaced by a nagging itch that mimics an insect bite or being stung by nettles.

Not everyone that comes into contact with the protein in the cercaria that triggers the condition will have a skin reaction (estimated at 30% to 40% of all people show a reaction).


Your doctor will want to know what you have been doing before you broke out into a rash. Once you mention swimming, they will typically give your rash a closer inspection for the telltale signs of swimmer’s itch: small red pimples that may develop into blisters. There are no specific blood tests available to test fo rthe condition.  Unfortunately, you may be itching for up to a week, but there are things you may do to ease the swimmer’s itch.

Swimmer's Itch on Arm - Example 3Swimmers Itch Picture
Photo Credit:

It is possible that the diagnosis for swimmer's itch can get confused with other skin conditions such as herpes, poison ivy, chicken pox or a bacterial skin infection (impetigo).


Most cases of swimmer’s itch will dissipate on its own, but if you do scratch and it gets worse, see your doctor for help. There are certainly several things you may try at home:

  • Cold compresses
  • Baking soda in a luke warm bath
  • Baking soda paste dabbed on the rash
  • Honey paste applied on the rash
  • Corticosteroid creams/lotions
  • Anti-histamines
  • Calamine lotion
  • Colloidal oatmeal in a luke warm bath
  • Oral antibiotics if your rash becomes infected from scratching.

There is no way to completely prevent swimmer's itch.  The risk can be reduced by avoiding shallow water (if swimming off a boat, move into deeper water),  towel drying after leaving the water, and avoid feeding and attracting water fowl such as geese.  More information is available on this swimmers itch fact sheet (PDF download).  

The application of copper sulfate will reduce the snail population, which will temporarily reduce the incidence of this problem.  Use of this product in waterways is tightly regulated and must be approved by your local fisheries office.

Swimmer's Itch on Legs


by: Brochure on the symptoms, treatment and prevention of Swimmer's Itch.

Brochure on the causes, symptoms, treatment and prevention of Swimmer's Itch.


Minnesota Department of Health