Dog HealthCat HealthGeneral Pet Care
What Is Ringworm (Dermatophytosis)?
Definition
Ringworm is a fungal skin infection, not a worm, caused by dermatophyte fungi (most commonly Microsporum canis in pets). It causes circular patches of hair loss, scaling, and sometimes mild itching. Ringworm is zoonotic — it can spread between pets and humans, and between different animal species. Children, the elderly, and immunocompromised people face the highest risk of human infection.
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Understanding Ringworm (Dermatophytosis)
The fungi responsible for ringworm infect the dead outer layer of the skin, hair follicles, and nails, feeding on keratin. Despite the name, there is no worm involved — the ring shape comes from the circular pattern of fungal growth spreading outward from the infection point. The condition was named before the causative organism was understood.
In dogs, ringworm typically causes circular patches of hair loss, often with a slightly scaly, reddened centre. In cats, it is often less dramatic — cats can carry the fungus without obvious lesions and act as asymptomatic carriers, which is particularly important in households with vulnerable human members. Kittens, long-haired cats, and Persian cats appear to be more susceptible.
Diagnosis is confirmed through fungal culture (the gold standard — takes 10–14 days), Wood's lamp examination (causes some strains of M. canis to fluoresce greenish under UV light, though not all strains do), or PCR testing. Treatment typically involves a combination of topical antifungal treatment to the affected areas and oral antifungal medication for widespread cases. Environmental decontamination is essential — fungal spores survive in the environment for up to 18 months.
📌 Key Facts
Caused by
Fungi (Microsporum canis most common) — NOT a worm
Zoonotic
Yes — spreads to humans, particularly children and immunocompromised
Environmental survival of spores
Up to 18 months
Diagnosis gold standard
Fungal culture (10–14 days)
Frequently Asked Questions about Ringworm (Dermatophytosis)
My child has a ringworm ring on their arm — could it have come from our cat?
Yes, very possibly. Cats, especially kittens and long-haired breeds, commonly carry Microsporum canis and can transmit it to humans through contact. Your cat should be examined by a vet and treated even if they have no visible lesions, as asymptomatic carrier cats are common. Meanwhile, avoid direct contact between the infected skin and other people.
Does ringworm need veterinary treatment or will it clear up on its own?
Mild cases in immunocompetent pets may self-resolve in 60–100 days, but treatment is still recommended to reduce the duration, prevent spread to other pets and humans, and address environmental contamination. Given the zoonotic risk, treatment rather than watchful waiting is the responsible approach.
How do I decontaminate my home after ringworm?
Vacuum regularly and discard vacuum bags, as spores survive. Wash pet bedding at high temperatures (60°C / 140°F). Clean hard surfaces with a diluted bleach solution (1:10). Remove and replace contaminated soft furnishings if possible. Environmental decontamination must be ongoing for the duration of treatment — typically several weeks.
⚠ Medical Disclaimer: This glossary entry is for educational purposes only
and does not constitute veterinary advice. Always consult a licensed veterinarian for diagnosis
and treatment of your pet's health conditions.