FAQ Frequently asked questions about bathing dermatitis (cercariae)

cercariae

Cercariae are microscopic larvae of sucking worms that require other living organisms, known as "intermediate hosts" and "final hosts", for their development and reproduction. The first larval stage colonises freshwater snails. In summer, it is swarming season, which means that the cercariae leave the snails and search for their definitive host. Here, they develop into flukes and lay new eggs. Cercariae usually colonise ducks as their final host. They become flukes, which lay eggs. The ducks excrete the eggs in their faeces. The eggs hatch into new larvae.

Swimmer's itch is a skin reaction triggered by cercariae. When cercariae come into contact with people in the water, they can mistakenly seek humans as hosts and burrow into the skin of bathers.
There they die as a result of the body's immune response. This causes itchy redness (wheals), similar to mosquito bites. The itching can begin within a few minutes of the cercariae entering the skin and subsides after 7 to 10 days at the latest. Bathing dermatitis is an unpleasant but harmless skin condition with no long-term effects.

The symptoms manifest as itchy, red patches on the skin, which often appear after swimming in shallow water. These red patches can develop minutes to hours after bathing. The itching can last for 7-10 days.

• If possible, shower immediately after swimming and rub your skin vigorously to remove any larvae.
• Avoid shallow water, especially if you know that cercariae are present.
• Do not feed water birds, as their faeces contain the eggs from which the larvae develop.

Cooling gels or creams can relieve the itching. If symptoms are severe, it is advisable to consult a dermatologist.

Cercariae can only survive in water for 2 to 3 days. The risk of contracting bathing dermatitis is therefore only present for a limited period of time.

Water birds such as ducks carry the eggs from which the larvae that cause bathing dermatitis develop. If you feed ducks, you attract them. This creates the risk that the eggs will be excreted into the water.

Cercariae can occur in any lake, especially in areas with shallow, warm water where water birds congregate.

In most cases, bathing dermatitis heals on its own. If the itching is very severe, the symptoms persist for more than 10 days or you notice a severe skin reaction, you should consult a doctor.