Brief overview
- Description: Itchy skin rash after swimming in fresh water, caused by the penetration of certain sucking worm larvae (cercariae) into the skin.
- Treatment: Antipruritic and anti-inflammatory ointments, gels or lotions (rarely also ointments containing cortisone) and cold compresses. If the itching is severe, the doctor will prescribe antihistamines (anti-allergic medication).
- Causes: Parasites (cercariae) that penetrate the skin when swimming in fresh water and lead to an inflammatory skin reaction.
- Symptoms: After swimming, a tingling and itching sensation appears on the skin, later reddened and raised patches (wheals) and small skin nodules (papules).
- Diagnosis: Consultation with the doctor, examination of the skin, blood test if necessary. The doctor usually recognizes bathing dermatitis from the typical symptoms and the appearance of the skin after swimming.
- Course: The skin changes often disappear on their own within a week to 20 days. Severe allergic reactions with dizziness, fever and shock are rare.
- Prevention: Avoid shallow waters, shower well and dry off after swimming, change wet swimwear, apply waterproof sunscreen.
What is bathing dermatitis?
These penetrate up to a few millimeters deep into the skin, where they trigger the typical symptoms. Normally, the parasites only attack waterfowl and certain water snails in order to reproduce. In humans, they dock on by mistake, as they cannot reproduce here and die after a short time. Humans are a so-called false host.
Children, who usually spend time in shallow water, and allergy sufferers are particularly affected by bathing dermatitis. The infestation of bodies of water with cercariae is increasing worldwide.
In common parlance, bathing dermatitis is also known as duck fleas, duck worm disease, dog bites or pond bites.
What are cercariae?
The larvae of sucking worms are known as cercariae. These are parasites that are barely or not at all visible to the naked eye in water. Cercariae normally infest waterfowl.
The parasites stay on the surface of the water on hot, sunny days and try to enter the bloodstream of waterfowl via the skin and blood vessels in their webbed feet. The cercariae have small suckers (hence the term sucking worms) on their abdomen and head, which make it easier for them to “dock” onto the host.
Occasionally, the larvae also bore into the skin of humans. They then cause an itchy rash on the skin – bath dermatitis develops.
Cercariae, which cause bathing dermatitis, are found in freshwater lakes (bathing lakes) in this country. They particularly prefer stagnant, shallow and warm water. They survive there for about two to three days. The larvae usually stay on the surface of the water.
The larvae usually hatch in early summer and reproduce mainly at temperatures above 24 degrees Celsius. Long-lasting summer weather with water temperatures above 20 degrees Celsius generally promotes the development and reproduction of the larvae.
Even if there are many waterfowl and water snails in the areas, this favors the spread of the cercariae, as these animals serve as hosts for the parasites. The larvae also like to live in reed beds and areas with lots of aquatic plants.
The unpleasant but largely harmless bathing dermatitis has nothing to do with a parasitic disease that is also caused by cercariae – schistosomiasis. This is a serious disease caused by the parasitic larvae of the pair fluke. This is native to the tropics and subtropics.
Cercariae do not occur in chlorinated water, such as outdoor swimming pools or pools.
How is bathing dermatitis treated?
Anti-inflammatory creams and gels
Home remedies
Home remedies such as cold compresses, essential oils (e.g. menthol or cineole) and aloe vera or witch hazel gel also help with bath dermatitis. They cool, soothe and relieve itching.
Cooling pads placed on the affected skin area also help to relieve itching. Important: Wrap the pad in a towel to prevent cold damage to the skin.
Home remedies have their limits. If the symptoms persist over a longer period of time, do not get better or even get worse, you should always consult a doctor.
Antihistamines
If the symptoms are more severe, the doctor may prescribe antihistamines (anti-allergic agents) in the form of gels or roll-ons (e.g. with the active ingredients mepyramine or diphenhydramine), which the patient applies to the skin. In severe cases, he prescribes anti-allergic medication in the form of tablets, drops or solutions (e.g. with the active ingredients cetirizine, loratadine or fexofenadine), which the patient takes.
It is not necessary to fight the larvae with antibiotics or special anti-parasite medication, as they die shortly after invasion.
Cortisone
Do not scratch
It is important not to scratch if you suffer from bath dermatitis: Otherwise injuries to the skin will occur, which may become infected with bacteria.
If severe allergic reactions such as dizziness, sweating, fever and/or nausea occur after bathing, these must be treated immediately. Call an emergency doctor immediately!
What causes bath dermatitis?
The skin symptoms of cercaria dermatitis are caused by the larvae of various types of sucking worms (trematodes, schistosomes), which inadvertently choose humans as their host. Normally, waterfowl serve as the worm’s main hosts and snails as intermediate hosts.
The larvae grow into worms in waterfowl (e.g. mallard ducks) and produce eggs there. The worm eggs enter the water via the feces of the worm-infested waterfowl. They hatch into small larvae, which normally infest a specific freshwater snail.
The larvae multiply in the snail and are released back into the shallow water after a few weeks. The new generation of larvae (cercariae) then go in search of waterfowl (especially ducks), which they infest and in whose intestines they develop into adult worms.
Only the second time – when the immune system recognizes the intruder – does the body react with a stronger immune response, which leads to the typical skin rash and severe itching.
The occurrence of cercariae is not related to the hygienic water quality of bathing lakes.
What does bathing dermatitis look like?
After the larvae have penetrated the skin, those affected experience a tingling, prickling, slight itching or burning sensation – similar to a mosquito bite. Red spots appear on the affected areas. These symptoms also occur when cercariae infest the body for the first time.
In sensitized people who are attacked by the parasites a second time, the actual skin rash (dermatitis) appears after around ten to 25 hours, sometimes over the entire body: this is accompanied by severe itching, much more intense than a mosquito bite, for example. In addition, reddened, swollen wheals (dot-shaped to plateau-shaped elevations of the skin) and papules (round to oval nodules) form on the affected areas of skin.
In particularly sensitive (allergic) people or in the case of a severe infestation with cercariae, it is also possible in rare cases that additional symptoms such as swelling of the lymph nodes, fever, nausea and/or circulatory disorders or even shock may occur.
Bath dermatitis is not contagious. Swallowing bath water does not cause cercaria dermatitis either. Cercariae only enter the body through the skin.
How does the doctor make the diagnosis?
If you suspect that you are affected by bath dermatitis, it is best to consult your family doctor or dermatologist. The doctor will make a suspected diagnosis based on the typical symptoms such as itching and the appearance of the skin (e.g. wheals, reddening of the skin, papules).
When talking to the doctor (anamnesis), it is particularly important to know that you have previously spent time in open water. Not least to rule out other skin diseases such as insect bites or other allergies.
The doctor can diagnose bathing dermatitis with certainty through a microbiological examination of the bathing water – and a blood test, in which he tests the affected person’s blood for antibodies against larval components.
If bathing dermatitis occurs more frequently in swimmers and bathers regionally and over time, this gives the doctor further clues.
How dangerous is bathing dermatitis?
The skin rash caused by bathing dermatitis is unpleasant for those affected due to the severe itching, but is generally harmless. The skin changes often heal on their own within a week, at the latest after 20 days, without any consequences.
If those affected scratch the wheals, infections can develop. Healing then usually takes longer.
Bath dermatitis can, however, progress very differently from person to person. It also varies in severity from person to person. Sensitive (hypersensitized) allergy sufferers may experience fever and shock, which must be treated immediately by a doctor.
How can you prevent it?
To protect yourself from cercaria dermatitis, certain behavioral measures are helpful when swimming in open water. Please note the following:
- Cercariae are mainly found in warm shallow water. You should therefore avoid shallow shore areas. If you swim a little further out, you are safe in deeper and cooler waters.
- Do not spend too long in shallow waters. Several shorter swimming intervals reduce the risk of cercariae infesting the skin.
- After bathing, it is important that you dry yourself well. Toweling your skin removes the larvae.
- It is best to change out of wet swimwear immediately.
- Rubbing waterproof sun creams into the skin also offers a certain degree of protection. This makes it more difficult for the parasites to penetrate the skin.
- As a preventative measure, it is also advisable not to feed ducks at bathing areas to avoid attracting the animals. The more ducks there are, the higher the risk of a cercaria infestation.
