Swimmer's Ear and Swimmer's Itch (Cercarial Dermatitis)

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Swimmer's Ear and Swimmer's Itch (Cercarial Dermatitis)


Disease History, Characteristics, and Transmission

Scope and Distribution

Treatment and Prevention

Impacts and Issues



Swimmer's ear (otitis externa) is an infection of the ear canal and swimmer's itch (cercarial dermatitis) is an allergic reaction to various types of microscopic waterborne parasites infecting human skin.

Many different types of fungi or bacteria can infect the ear canal—the hollow cylindrical-like opening that allows sounds to enter the eardrum. Swimmer's ear often results.

Swimmer's itch—sometimes also called duck itch and clam digger's itch in the United States and various other names around the world—is a distinctly different infection caused by parasitic schistosomes (small flukes that live in blood) that infect snails and vertebrates. Most schistosomes infect waterfowl. The parasites are discharged from infected snails and vertebrates into fresh waters (often slow-moving ponds and lakes). The parasites then burrow into the skin of swimming humans. They cause an allergic reaction, itch, and rash.

These schistosomes cannot become long-term parasites in humans. They only cause mild itchy spots, which later can become raised bumps that are much itchier. The parasites die within a few hours, and the symptoms disappear.

Disease History, Characteristics, and Transmission

Swimmer's ear occurs frequently in children because they usually spend more time swimming. It can also occur in environments with high humidity. The infection can also arise any time a break in the skin occurs within the ear canal. Thus, any extended exposure to moisture in the ear often irritates the ear canal, which allows fungi or bacteria to enter. People often get swimmer's ear when they have dry skin or eczema, frequently or aggressively scratch or clean the ear canal, or insert objects into the ear canal, such as cotton swabs, pencil tips, or paper clips.


MALIGNANT: A general term for cells that can dislodge from the original tumor, invade and destroy other tissues and organs.

PARASITE: An organism that lives in or on a host organism and that gets its nourishment from that host. The parasite usually gains all the benefits of this relationship, while the host may suffer from various diseases and discomforts, or show no signs of the infection. The life cycle of a typical parasite usually includes several developmental stages and morphological changes as the parasite lives and moves through the environment and one or more hosts. Parasites that remain on a host's body surface to feed are called ectoparasites, while those that live inside a host's body are called endoparasites. Parasitism is a highly successful biological adaptation. There are more known parasitic species than nonparasitic ones, and parasites affect just about every form of life, including most all animals, plants, and even bacteria.

SCHISTOSOMES: Blood flukes that infect an estimated 200 million people.

Trichobilharzia and Gigantobilharzia are two genera of schistosome that commonly cause swimmer's itch. These schistosomes infect waterfowl, such as ducks and geese, and aquatic mammals, such as beavers. The parasites lay eggs that are transferred in the feces of infected birds or mammals. The eggs, if dropped into water, hatch and release larvae that can infect humans.

Schistosomatium douthitti is a species of schistosome that infects snails. It first infects a non-human vertebrate, such as a waterfowl or mammal, and completes its lifecycle within these hosts. However, humans can become indirectly infected when coming into contact with infected waters or shorelines.

Symptoms of swimmer's ear include fever, skin inflammation inside the ear canal, temporarily reduced hearing (caused by swollen tissue), and itchiness. More severe symptoms include reddening and swelling of the outer ear, enlarged and tender lymph nodes around the ear, and yellowish drainage. Sharp pain often affects the earlobe or other external parts. In severe cases, the skin infection spreads to the face and salivary gland in the cheek. Eating can become painful. According to the Nemours Foundation, swimmer's ear is not contagious.

Swimmer's itch has symptoms that occur from minutes to days after contact. Common symptoms include mild itchy areas on the skin, which can become more itchy and redder after a few hours. There is also a tingling or burning sensation in the infected areas. Later, small blisters can appear. Itching usually stops within a week and other symptoms gradually disappear. Children are more likely to become infected due to the simple fact that they spend more time around water. According to the U.S. Centers for Disease Control and Prevention, swimmer's itch cannot be spread from person to person.

Scope and Distribution

Swimmer's ear is found is all temperate climates of the world where water is available for swimming. It is considered an infection that frequently occurs.

Swimmer's itch occurs throughout the world. The parasites causing the infection are more frequently found around lakes or other such bodies of slow-moving fresh and salt water. Inshore waters, rather than open waters, are more likely to contain schistosomes. They commonly infect humans during the hotter months of the year, and often infect humans that wade or swim close to shore or in shallow water.

Treatment and Prevention

Treatment of swimmer's ear includes using over-the-counter drops of a dilute solution—usually about 2%—of acetic acid or alcohol. Such ear drops are usually used several times a day for a maximum of ten days. Care should be taken because improper use can irritate or damage membranes located past the ear canal. Ear drops containing quinolone antibiotics are useful for stopping fluid discharge and combating bacterial infection. A corticosteroid is used to prevent inflammation, itching, and swelling. Treatment usually will cure the problem within seven to ten days.

Swimmer's ear can be prevented by drying a child's ears with a towel. Battery powered ear dryers can also be used. The child's head also can be tilted to the side so that excess water runs out. Doctors may recommend earplugs while swimming; however, the earplugs should be professionally fitted because they can irritate the ear canal if improperly used. Until the infection has cleared up, doctors recommend that a child should not swim or wash his or her hair. To prevent damage to the ear canal, children should not be allowed to place objects in their ears or to clean their ears themselves.

The American Osteopathic College of Dermatology recommends that swimmer's itch be treated with an antihistamine cream or a mild corticosteroid cream. Both can be purchased as over-the-counter medicines. However, if symptoms, such as scratching, continue longer than three days, the AOCD recommends a visit to a dermatologist.

Prevention of swimmer's itch usually involves the long-term removal of the schistosome hosts. For instance, various control agents such as copper sulfate have been used to eliminate snail populations around lakes. The application of the insect repellant DEET (N, N-diethylm-toluamide) to the body can help to repel schistosomes.


The external ear consists of the flesh and cartilage structure on either side of the head, known as the auricle or pinna, and of the hole into the head. The auricle helps focus the incoming sound waves. The hole leads into the auditory canal, a roughly cylinder-shaped, small diameter canal that is about 2.5 cm long. Towards the inner end, the canal widens slightly and ends at the eardrum. The ear canal can be thought of as a shaped tube with a resonating column of air inside it, having open and closed ends, similar to the construction of an organ pipe.

This analogy is apt, for the ear canal enhances the sound vibrations that have traveled in from the outside. The canal can resonate, or vibrate, typically at frequencies that the ear hears most sharply. The vibration increases the wavelength of the sound waves traveling down the canal. The amplified waves eventually contact the ear drum, which is positioned at the inner end of the canal, and marks the boundary between the outer ear and the middle ear.

The ear drum is a membrane. It is capable of vibration, which occurs when the sound waves contact it. The vibrational energy of the ear drum is converted to mechanical vibrations in the solid materials of the middle ear. These solid materials are three bones: the malleus, incus and stapes. The bones form a system of levers that are linked together and are driven by the eardrum. The outer malleus pushes on the incus, which in turn pushes on the stapes. This further amplifies the sound vibrations, typically 2–3 fold. Muscles are positioned around the bones, the smallest muscles in the body, and ‘dampen down’ the mechanical vibrations if they become too pronounced. They are a form of safety device, restricting movement of one or more of the bones. This protects against the creation of too great a vibration from a very loud sound.

Impacts and Issues

People with diabetes or immune system disorders should get medical assistance immediately when affected with swimmer's ear. They are more likely to suffer severe symptoms including malignant otitis externa, which is a rare form of otitis externa. Rather than staying on the surface of the outer ear, this disease can move into the bony structures of the ear and may permanently destroy them.

Because marine pollution is increasing around the world, especially in developed and developing countries, more incidents of swimmer's itch are occurring. In addition, global warming is creating conditions favorable to expanded populations of water-borne parasites. Many people have more leisure time and may choose to spend this time around water. More people are also moving to areas containing slow-moving bodies of water, such as lakes and estuaries. The rate of swimmer's itch increases both with the amount of time spent in infected waters and with the level of pollution in waters where swimming is done.

See AlsoEar infections (Otitis Media); Water-borne Disease.



Bluestone, Charles D. Targeting Therapies in Otitis Media and Otitis Externa. Hamilton, Ontario, Canada: Decker DTC, 2004.

Zhai, Hongho, and Howard I. Maibach. Dermatotoxicology. New York: CRC Press, 2004.


Beers, S., and T. Abramo. “Otitis Externa Review.” Pediatric Emergency Care 20 (April 2004): 250–256.

Verbrugge, L. M., et al. “Prospective Study of Swimmer's Itch Incidence and Severity.” Journal of Parasitology 90 (2004): 697–704.

Web Sites

Centers for Disease Control and Prevention. “Cercarial Dermatitis.” September 17, 2004. <http://www.cdc.gov/ncidod/dpd/parasites/cercarialdermatitis/factsht_cercarialdermatitis.htm> (accessed March 24, 2007).

Health Canada. “Material Safety Data Sheet—Infectious Substances: Ascaris lumbricoides.” January 23, 2001. <http://www.phac-aspc.gc.ca/msds-ftss/msds9e.html> (accessed March 23, 2007).

KidsHealth for Parents. “Infections: Swimmer's Ear.” March 2006. <http://www.kidshealth.org/parent/infections/ear/swimmer_ear.html> (accessed March 27, 2007).