Children's Hospital Colorado

Swimmer's Itch - Lakes and Oceans

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  • An itchy harmless rash caused by tiny parasites in fresh water lakes
  • Less commonly occurs in salt water (called clam digger's itch)

Symptoms of Swimmer's Itch

  • Itchy skin rash
  • Begins within 2 hours of swimming in a fresh water lake. It can also occur in salt water, although this is less common.
  • The rash only occurs on areas exposed to the lake water. The legs are commonly involved. The bathing suit area may be spared.
  • The first symptom is itching or burning of the skin.
  • Then small red spots appear within 1 or 2 hours. The spots appear at sites where a parasite has gotten into the skin.
  • The spots turn into small red lumps over 1 or 2 days.
  • The spots can be quite itchy for up to 7 days. The rash gradually fades away over 2 weeks.
  • Also called cercarial dermatitis


  • Swimmer's itch is caused by a very tiny parasite. (You can only see it with a microscope). It gets into the skin of humans by mistake.
  • The rash and itching are the body's allergic reaction to parasites in the skin.
  • This parasite can be found in lakes in every state (US). It is also found in lakes in Canada and over 30 other countries. In the US, Michigan and other Great Lakes region states are most involved.
  • It is less common in salt water (called clam digger's itch).
  • The parasites get into the lakes from the droppings of water birds. Their normal life cycle involves birds and snails. It dies off quickly in human skin.

Repeat Contact (Exposure) and the Body's Reaction

  • Swimmer's itch is the body's allergic reaction to the parasite. Each time the body is exposed, the more intense the reaction will be. This is called sensitization.
  • After first-time contact, the onset of itching and rash takes 1 to 2 weeks.
  • For repeat contact, the onset of itching and rash is within 2 hours.
  • The more the exposures, the faster the rash occurs. It also causes the rash and itching to become more severe.

Call Doctor or Seek Care Now

  • Spreading red area or streak with fever
  • Spreading red area or streak that's very large
  • Your child looks or acts very sick

Contact Doctor Within 24 Hours

  • Spreading red area or streak, but no fever
  • Severe past allergic reaction to lake swimming that needed oral steroids
  • You think your child needs to be seen

Contact Doctor During Office Hours

  • Severe itching not better after 24 hours of using steroid cream
  • Scab that looks infected (drains pus or gets bigger). Care Advice: apply an antibiotic ointment 3 times per day until seen.
  • Swimmer's itch lasts more than 2 weeks
  • You have other questions or concerns

Self Care at Home

  • Swimmer's itch suspected. (Itchy rash that starts within 2 hours of being in a lake or ocean)

Care Advice for Swimmer's Itch

  1. What You Should Know About Swimmer's Itch:
    • Swimmer's itch is caused by a small parasite found in many lakes. It is less common in salt water. The parasite normally only attacks water birds.
    • The main symptoms are itching and a rash.
    • For swimmers, the rash can be widespread.
    • For children who wade, the rash may occur only on the legs.
    • No specific medicine is needed. Reason: The parasites die once they pass into the skin. The itching is a temporary allergic reaction.
    • Here is some care advice that should help.
  2. Steroid Cream for Itching:
    • To help with the itch, put 1% hydrocortisone cream (such as Cortaid) on the rash. No prescription is needed. Use 3 times per day.
    • Baking soda paste is another option. Make this by putting baking soda into a cup. Slowly, stir in water until it reaches a thickness like paste. Put it on the itchy spots as needed.
  3. Cold Pack for Itching:
    • Put a cold pack on the most itchy spots. You can also use ice wrapped up in wet washcloth.
    • Do this for 20 minutes 4 times a day.
  4. Allergy Medicine for Itching:
    • For severe itching, give an allergy medicine (such as Benadryl). Give it 4 times per day. No prescription is needed.
    • Caution: Do not use if age is under 1 year. Reason: Benadryl is a sedative. Give your doctor a call for advice.
  5. Try Not to Scratch:
    • Help your child not to scratch.
    • Cut the fingernails short.
    • Reason: Prevents a skin infection from bacteria.
  6. What to Expect:
    • The spots turn into small red lumps over 1 to 2 days.
    • The spots can be quite itchy for up to 7 days.
    • The rash gradually fades away over 2 weeks.
  7. Return to School:
    • The rash cannot be spread to others.
  8. Prevention of Swimmer's Itch:
    • Avoid swimming in areas where swimmer's itch has been a known problem.
    • Towel yourself dry right after swimming or wading. Reason: Wipe off parasites before they get under the skin.
    • The rash is usually worse with each exposure. So, it's very important to try to prevent recurrences.
  9. Call Your Doctor If:
    • Rash becomes infected
    • Itching becomes severe
    • Rash lasts over 2 weeks
    • You think your child needs to be seen
    • Your child becomes worse


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