Ringworm in Pets: What It Is, How to Treat It, and Protecting Your Family
Ringworm Is Not a Worm
Despite the name, ringworm (dermatophytosis) is a fungal infection — specifically caused by fungi in the genera Microsporum and Trichophyton. The name comes from the characteristic circular lesion pattern it sometimes creates, not any parasitic worm. It's one of the most common skin infections in cats and is also seen in dogs, and it's zoonotic — meaning it can spread from pets to humans. Understanding how it's transmitted, diagnosed, and treated prevents both prolonged pet suffering and household outbreaks.
How Ringworm Presents in Pets
The classic presentation in cats is one or more areas of circular hair loss, often with scaling or crustiness at the border and broken hairs. The lesions are often not itchy, which can make owners less likely to notice them or seek early care. Common locations include the head, ears, and forelimbs. In dogs, presentation is similar but often more variable.
An important complicating factor: not all ringworm looks like a ring, and many ringworm lesions are irregular in shape, small, or easily overlooked. Conversely, many skin conditions that look like ringworm are not. Diagnosis should always be confirmed by a veterinarian — a Wood's lamp examination (UV light that causes some but not all ringworm species to fluoresce), fungal culture, or PCR testing. Fungal culture is the gold standard but takes 10-14 days to grow.
Transmission
Ringworm spreads by direct contact with an infected animal or contaminated environment (fungal spores can survive on surfaces, bedding, and in carpet for months to over a year). Young animals, older animals, and immunocompromised individuals — whether pet or human — are at highest risk. Shelters frequently deal with ringworm in newly arrived kittens.
In humans, ringworm from pets causes itchy, scaly circular skin lesions, typically on the arms, neck, or face (areas of contact with infected pets). Scalp ringworm in children requires specific antifungal treatment. If anyone in your household develops skin lesions while a pet is being treated for ringworm, consult a human healthcare provider.
Treatment
Effective ringworm treatment requires a combination approach: treating the infected pet, decontaminating the environment, and protecting household members.
Pet treatment: Antifungal medication — typically oral itraconazole or terbinafine for cats, which are more effective than older treatments. Topical antifungal shampoos (miconazole/chlorhexidine) or lime sulfur dips used 1-2 times weekly significantly reduce environmental contamination by reducing fungal shedding. Treatment continues for several weeks — typically 2-4 weeks after resolution of clinical signs and negative fungal cultures.
Environmental decontamination: Wash all bedding in hot water weekly. Vacuum carpets frequently and discard vacuum bags. Wipe hard surfaces with a diluted bleach solution (1:10 bleach:water). Restrict the infected pet to easily-cleaned rooms during treatment to limit the scope of contamination.
Preventing Reinfection
Treatment failure is often related to inadequate environmental decontamination rather than inadequate medication. The fungal spores in carpet, upholstery, and air vents are a persistent reservoir that reinfects treated animals. Thorough, ongoing environmental cleaning throughout the treatment period is as important as the medication itself.