Ringworm in Dogs and Cats: Signs, Treatment, and Cost

Ringworm is one of those conditions that sounds worse than it is, yet causes more panic than most things I see at Hearthstone Animal Clinic. The name is misleading: there's no worm involved. Ringworm is a fungal infection of the skin, hair, and nails caused by dermatophytes, and yes, it can spread from your pet to you. Here in Cypress, TX, I diagnose ringworm year-round, though I see more cases in humid months and in multi-pet households. If you're looking at a bald patch on your dog or cat and wondering if ringworm is the culprit, this post will walk you through what I look for, what treatment actually involves, and when you should be concerned.

What exactly is ringworm and how do pets catch it?

Ringworm (dermatophytosis) is caused by fungal organisms, most commonly Microsporum canis in cats and dogs. These fungi feed on keratin, the protein in skin, hair, and nails. The "ring" in ringworm comes from the classic circular pattern the lesions can form on human skin, though this ring shape is actually uncommon in pets.

Pets pick up ringworm through:

• Direct contact with an infected animal (another dog, cat, rodent, or even wildlife)
• Contaminated environments like bedding, grooming tools, or kennels
• Fungal spores in soil, which can survive for months

Spores are remarkably hardy. They can live in carpet fibers, furniture, and brushes for 18 months or longer. This is why ringworm tends to bounce around in shelters, grooming facilities, and homes with multiple pets.

What does ringworm look like on dogs and cats?

This is the part most owners get wrong, and it's not their fault. Ringworm rarely looks like a neat circle on pets.

Signs in dogs

• Patchy hair loss, often starting on the face, ears, paws, or tail
• Scaly, crusty, or flaky skin in the bald areas
• Broken or brittle hair shafts at the edges of patches
• Mild redness or darkened skin
• Sometimes itchy, sometimes not

Signs in cats

• Circular or irregular bald patches, often on the head, ears, and forelimbs
• Excessive dandruff or scaling
• Broken whiskers
• Skin that looks slightly irritated or gray
• Some cats (especially longhaired breeds) are asymptomatic carriers, showing no signs while shedding spores everywhere

The itch factor varies wildly. Some pets scratch constantly, others seem unbothered. If your pet has hair loss with crusty edges and you recently adopted them, visited a groomer, or have other pets showing similar spots, ringworm should be on the list.

How do veterinarians diagnose ringworm?

I can't diagnose ringworm just by looking at it. Many skin conditions mimic it: bacterial infections, allergies, mites, even autoimmune diseases. Here's what I actually use:

Wood's lamp (black light)

About 50% of Microsporum canis infections will fluoresce apple-green under ultraviolet light. It's a quick screening tool, but a negative result doesn't rule ringworm out.

Fungal culture

This is the gold standard. I pluck hairs from the edge of a lesion and place them on a special culture medium. If dermatophytes grow, we have our answer. The catch: cultures take 7 to 21 days to turn positive. Patience is part of the diagnosis.

PCR testing

A faster option that detects fungal DNA, usually with results in 3 to 5 days. More expensive, but useful when you need an answer quickly (say, in a household with immunocompromised people).

According to the Companion Animal Parasite Council (CAPC), fungal culture remains the most reliable diagnostic method, though PCR is gaining ground in practice.

How is ringworm treated in pets?

Ringworm is curable, but treatment takes time. Most cases require a combination approach:

Topical therapy

• Antifungal shampoos containing miconazole or chlorhexidine, used 2 to 3 times weekly
• Antifungal creams or ointments applied directly to lesions
• Lime sulfur dips for widespread infections (effective but smelly, and they will stain light-colored fur yellow temporarily)

Topical treatment alone works for very mild, localized cases. For most pets, I also prescribe oral medication.

Oral antifungal medication

The most commonly used drugs are:

• Itraconazole: my first choice for cats, given daily or in a pulse protocol (one week on, one week off)
• Terbinafine: effective in both dogs and cats, generally well-tolerated
• Griseofulvin: older medication, still used but with more potential side effects

Treatment duration is typically 6 to 12 weeks minimum. I don't stop treatment based on how the pet looks. I stop when two consecutive fungal cultures come back negative, usually spaced 2 to 3 weeks apart. Stopping too early is the number one reason ringworm comes back.

How much does ringworm treatment cost?

Cost depends on severity and how many pets are affected. A rough range for a single pet at Hearthstone Animal Clinic:

• Initial exam and diagnosis: $65 to $150 (depending on whether we do culture, PCR, or both)
• Topical products: $20 to $50
• Oral medication (6 to 12 weeks): $80 to $200
• Follow-up cultures: $40 to $80 each

Total for a straightforward case: roughly $200 to $500. Complicated cases involving multiple pets or environmental decontamination can run higher. If you're curious about what to expect for other conditions, you can check our pricing page.

Can I catch ringworm from my pet?

Yes. Ringworm is zoonotic, meaning it passes between animals and humans. Children, elderly individuals, and immunocompromised people are at higher risk. On human skin, ringworm often does form that classic red, itchy ring.

If your pet is diagnosed with ringworm:

• Wash your hands after handling them
• Wear gloves when applying topical treatments
• Keep the infected pet in a room with hard floors that's easy to clean
• Vacuum daily and discard the bag (or empty the canister outside)
• Wash bedding, collars, and fabric items in hot water with bleach if safe for the material
• Disinfect hard surfaces with a 1:10 bleach solution

If anyone in your household develops suspicious skin lesions, see a physician. Most human cases are easily treated with topical antifungals, but early treatment prevents spread.

How do I prevent ringworm from spreading to other pets?

Isolation is key. Keep the infected pet in a separate area until treatment is complete and cultures are negative. In multi-pet homes, I often recommend prophylactic treatment (topical therapy) for all animals, even those not showing signs, since asymptomatic carriers are common, especially among cats.

Environmental cleanup is half the battle. Those spores are everywhere the infected pet has been. Aggressive cleaning during and after treatment makes the difference between one round of medication and an ongoing headache.

When should you bring your pet in?

If your dog or cat has unexplained hair loss, especially with scaling or crusting, it's worth getting a diagnosis. Ringworm won't resolve on its own, and the longer it goes untreated, the more spores spread through your home.

Bring your pet in sooner if:

• Multiple pets are showing similar signs
• You or a family member develops a rash
• Your pet was recently adopted from a shelter or rescue
• You have young children or immunocompromised individuals at home

If you're seeing patchy hair loss or crusty skin on your pet and you're not sure what you're dealing with, let's figure it out. You can schedule a visit at Hearthstone Animal Clinic in Cypress, TX, or reach us at (281) 859-9244. The sooner we diagnose it, the faster we can get your pet (and your household) back to normal.