"Ringworm" is the common name for the skin infection caused by a special group of fungi. It is not caused by a worm at all. The fungi feed upon the dead cells of skin and hair causing, in people, a classic round, red lesion with a ring of scale around the edges and normal recovering skin in the center.

Because the ring of irritated, itchy skin looked like a worm, the infection was erroneously named. The fungi responsible are called "dermatophytes," meaning "plants that live on the skin" thus the more correct term for ringworm is "dermatophytosis." The characteristic "ring" appearance is primarily a human phenomenon. In animals, ringworm frequently looks like a dry, grey, scaly patch but can also mimic any other skin lesion and have any appearance. It is often itchy in people but not always in pets.


The spores of dermatophyte fungi are extremely hardy and can live for years in the environment. Infection occurs when spores come in contact with broken skin or with an immune compromised individual. Most healthy animals can clear ringworm infections on their own over time. Infected animals can shed spore-covered hairs as infected hairs break off into the environment. Some animals are carriers, who never show signs of skin irritation themselves but can infect others readily. There are several species of dermatophyte fungi. Different species of fungi come from different kinds of animals or even from soil thus determining the ringworm species can help determine the source of the fungal infection.


Ringworm is contagious to people; however, some people are at greater risk than others. High risk individuals include the very young, the elderly, immune-compromised, and highly stressed animals and people. DIAGNOSIS Some types of ringworm will fluoresce green under a black light (Wood's light). A fungal culture is the confirmatory test for ringworm. To culture, some hairs and skin scales are placed in a special medium for 2-3 weeks. In cases highly suspicious of dermtophytosis, treatment may be started before results come back.


Treatment for ringworm can involve three aspects: * Fungal growth inhibitors (oral medications) * Topical treatment * Environmental Treatment

ORAL MEDICATION FOR INFECTED PETS (Fungal growth inhibitors)

Treatment with oral medication typically is continued for 3 weeks to 2 months and should not be discontinued until the pet cultures negative or 2-4 weeks after clinical signs have resolved. Stopping when the pet simply looks well visually frequently leads to recurrence of the disease. Most oral medications must be given with food, and should not be used in pregnant pets. Common oral medications include Itraconazole, Terbinafine, and Ketoconazole. (Previously used medications that are no longer considered effective include Griseofulvin and Lufenoron).


The above medications work by inhibiting fungal reproduction rather than by directly killing the fungus. To prevent reinfection, treatment should also reduce contamination of the environment. This means actually killing the fungus on the pet so that the hairs dropped will not be infectious.


Topical treatments generally are a combination of an antifungal (usually Miconazole or Ketoconazole) and Chlorhexidine. Sprays, mousse treatments, or ointments are all options. Your veterinarian may also recommend twice weekly antifungal shampoos or leave in conditioners. Be sure that you carefully follow the directions for these products. Shampoos should be allowed to soak for 10-15 minutes before rinsing. Leave-in conditioners should not be rinsed off.


If your veterinarian prescribes this, dips should be done twice a week. Wear gloves when using lime sulfur. If you attempt this kind of dipping at home, you should expect: * Lime Sulfur will stain clothing and jewelry * Lime Sulfur will cause temporary yellowing of white fur * Lime Sulfur smells strongly of rotten eggs. Follow prescribed directions and do not rinse off dip at the end of the bath. It can also be applied as a spray or wiped on with a sponge.


Environmental treatment focuses on decreasing fungal spores with cleaning (vacuuming and steam cleaning, being sure to throw away the vacuum bag after. For surfaces that can be bleached, bleach diluted 1:10 will kill 80% of fungal spores. To reduce environmental contamination, infected cats should be confined to one room until they have cleared the infection. The rest of the house can be disinfected during this confinement period.

Key Points:

  • Ringworm is a fungus, so it grows slowly and dies slowly
  • Most healthy animals can clear ringworm on their own over time
  • Spores can remain active in the environment for over 18 months
  • Successful treatment may require multi-modal treatment


Ringworm Pamphlet: https://www.wormsandgermsblog.com/wp-includes/ms-files.php?file=2008/04/M1-Ringworm-Owner.pdf

Ringworm: Environmental Cleanup: https://www.wormsandgermsblog.com/2008/10/articles/animals/cats/ringworm-part-2-cleaning-up/

Ringworm Environmental Decontamination in Homes of Dogs and Cats: https://veterinarypartner.vin.com/default.aspx?pid=19239&id=7058488

Ringworm in Dogs and Cats: https://veterinarypartner.vin.com/default.aspx?pid=19239&id=4951439