Cat ringworm: scale, broken hair and the infection that spreads to people

Quick answer

Brushing is where most owners first see it: scale in the coat, and hair that comes away in short broken pieces rather than full-length strands.

Most flaking in a cat's coat is not dry skin. It is a sign that something has changed in the skin, in the cat's ability to groom itself, or in what is living on the hair.

The one cause you cannot afford to guess at is ringworm, which is a fungal infection of the hair shaft rather than a worm. It spreads to other pets and to people in the house, it can look like almost nothing, and it is the only common cause of feline scaling that puts your family at risk.

• Ringworm breaks hairs rather than shedding them, so the giveaway is stubbly, uneven hair with scale, not a smooth bald patch.
• Ear tips, the muzzle, the bridge of the nose, the front legs and the tail base are the usual first sites.
• A cat can carry and spread it while looking almost normal, which is why long-haired cats from multi-cat homes are the classic silent source.
• Flaking only over the lower back and tail base in an older or heavy cat is usually not skin disease at all: it means the cat can no longer reach that area.
• Any new scaly, itchy, ring-shaped lesion on a human in the household changes the priority from routine to urgent.

Decide in 60 seconds

Why the coat breaks rather than falls out

Dermatophytes are fungi that live on keratin, the structural protein of hair, claw and the outer skin layer. They do not invade living tissue in a healthy animal.

The fungus grows down the hair shaft from the surface and digests it from within. A hair that has been hollowed out this way loses its tensile strength and snaps under ordinary friction: grooming, rubbing on a door frame, a cat flap.

That mechanism explains almost everything an owner sees.

Hair does not fall out cleanly, so the patch looks stubbly and uneven rather than bald. Scale appears because the fungus disrupts the normal shedding of the outer skin layer. And the broken hair fragments, each carrying spores, are the vehicle that moves the infection onto bedding, sofas, carpets and clothing.

It also explains why the cat is often not very itchy. This is a surface infection of dead tissue, not an allergic reaction, so many cats show no discomfort at all. Owners who wait for scratching wait too long.

The infection tends to appear first where hair is short, where the coat is thin and where the cat rubs against things: the tips of the ears, the muzzle, the bridge of the nose, the fronts of the forelegs and the tail base.

What a healthy coat and skin look like

Part the coat against the direction of growth in good daylight, over the shoulders, along the spine, at the tail base, on the belly and inside the thighs.

Healthy skin is uniform, without redness, greasiness or crust. There is little visible scale, and what there is dusts off rather than sitting in plates.

Hair should be even in length within a region. Run your fingers backwards through it: full-length hairs come away in the comb, but you should not find a crop of short broken stubs.

Ear margins should be smooth, with fine even fur to the edge. A moth-eaten ear tip with scaly skin behind it is a real finding, not cosmetic.

Whiskers and the hairs of the eyebrows should be intact. Broken or missing whiskers on one side of the face are worth a second look.

Skin colour varies with the cat, but any area that is newly red, thickened, greasy or crusted has changed for a reason.

Ranking the causes of a flaky coat

Ringworm.

Multifocal scale with broken hairs, often on the face, ears and limbs. Frequently mildly itchy or not itchy. Kittens, cats from shelters and catteries, long-haired cats and outdoor hunters are over-represented. This is the one that infects people.

Cheyletiella, sometimes called walking dandruff.

Large scale, concentrated along the back, which appears to move because the mites carry it. Usually itchy in both cat and owner. Common in kittens and in homes with rabbits.

Fleas and flea allergy.

Classic pattern is small crusted bumps along the back and around the neck, with hair loss at the tail base. Flea dirt combs out as dark grit that turns rust-red on damp paper. A cat can be flea allergic with almost no fleas visible.

The cat that can no longer reach.

Scale and matting strictly over the lumbar spine, hips and tail base with a normal coat elsewhere is a mobility sign. Arthritis and obesity are the two big causes, and both are under-diagnosed in cats because a stiff cat simply jumps less rather than limping.

Systemic disease.

An unkempt, greasy or dull coat over the whole body in a middle-aged or older cat often reflects illness rather than skin disease. Weight loss, thirst change, appetite change or vomiting alongside a poor coat all point towards an internal cause and a blood test rather than a shampoo.

Overgrooming.

Hair broken off at skin level over the belly, flanks or forelegs, with normal skin underneath and no scale. Cats do this so privately that owners often insist it is not happening. Hair in the vomit or faeces is the tell.

Autoimmune and drug-related disease.

Pemphigus foliaceus produces crusts with a marked preference for the nose, ear flaps and the skin around the claws. It is uncommon but it is treated in a completely different way, so it must not be assumed to be ringworm.

Changes that mean act today

A human lesion in the house.

A new itchy, expanding, ring-shaped patch on an arm, neck or trunk of someone who handles the cat should be assumed related until proven otherwise. It usually appears where the cat is held.

Rapid spread in a kitten.

Kittens have immature immunity and a low reserve. Widespread lesions with crusting and secondary bacterial infection can develop within days.

Nodules rather than patches.

Firm lumps in the skin, particularly in Persians and related breeds, can be a deep form of the infection that sits under the skin rather than on it. It does not respond to ordinary treatment and often needs surgery as well as prolonged medication.

Any lesion in an immunosuppressed cat.

Cats positive for feline immunodeficiency virus or feline leukaemia virus, cats on steroids or chemotherapy, and cats with poorly controlled diabetes all lose the ability to contain the infection.

How it is confirmed, and why one test is not enough

Everything in this picture becomes contaminated. Brushes, combs, towels and bedding used on an infected cat carry spores on hair fragments and must be cleaned or replaced, not shared with other pets.

A Wood's lamp is a screening tool, not a diagnosis. Only some strains of Microsporum canis fluoresce, the fluorescence belongs to the hair shaft rather than to scale or claw, and lint, sebum and topical products all produce misleading glows. A negative lamp is close to meaningless.

Direct microscopy of plucked hairs can show the fungus around the shaft and gives an answer in minutes when it is positive.

Fungal culture remains the reference test. It is slow, taking days to weeks, but it identifies the organism, and repeat cultures are the accepted way to prove that treatment has worked.

PCR is fast and sensitive. Its limitation matters: it detects fungal DNA whether the organism is alive or dead, so a positive result late in treatment does not necessarily mean ongoing infection.

Tell the vet if you have already applied anything. Creams, shampoos and disinfectants suppress culture growth and waste the test.

What the vet will want from you.

Where the cat came from and when, whether it is from a shelter, cattery, breeder or the street, how many other animals are in the house, whether the cat hunts or goes outside, whether any human has a lesion, what you have already applied, and any photographs of the lesions when they first appeared.

Treating it properly, which means three things at once

Systemic medication.

An oral antifungal reaches the fungus inside the hair follicle, where topical products do not. Which drug is used depends on your country, on licensing and on the cat's other conditions. Some older options are teratogenic and unsuitable around pregnancy. This is a prescription decision, and it runs for weeks, not days.

Whole-body topical treatment.

Topical therapy is what reduces the shedding of infective spores into your home. It must be applied to the whole cat, not to the visible patch, because unaffected-looking coat carries spores. Products differ by region and some are irritant or unsuitable for kittens, so follow the product your vet dispenses rather than something bought online.

Environmental decontamination.

The infective material is hair fragments. Mechanical removal does most of the work: vacuum daily, wash textiles at the hottest temperature the fabric allows, and either wash or discard soft items that cannot be cleaned. Disinfectant only works on a surface that has already been cleaned of hair and organic debris.

Confining the cat to one easily cleaned room while it is most infective reduces the size of the problem enormously and shortens the total decontamination effort.

The routine that catches skin problems early

The ear margin is the single most useful place to look. Ringworm often starts here as a thin, scaly, moth-eaten edge long before anything appears elsewhere.

Two or three photographs taken a week apart tell a vet more than any description. Lesions that are expanding at the edge, and lesions that are appearing in new places, are the ones that need faster action.

What never to do

Do not decide it is dry skin and add oil supplements. Fat supplements help genuine dietary deficiency and do nothing at all for a fungal infection, while the delay lets it spread.

Do not use a human antifungal cream on a cat without advice. Cats groom it off and swallow it, some human formulations are not safe by mouth, and partial treatment makes later diagnosis harder.

Do not clip the coat casually. Clipping can spread the infection into the microtrauma the blades create, and contaminated clippers move it around the household. If clipping is needed, it is a decision made with your vet and with strict cleaning afterwards.

Do not share brushes, combs or bedding between animals during an outbreak.

Do not treat only the affected cat in a multi-pet home. Dogs, rabbits and other cats in contact all need assessment, because untreated carriers restart the cycle.

Do not stop treatment when the coat looks better. Regrowth appears well before the fungus has gone, and this is the single most common cause of relapse.

When to get help

The end point is a cat with an even coat, no scale and repeated negative tests, in a home that has been cleaned of the hair fragments that carry spores.

Book a same-day or urgent appointment if the cat is a young kitten with spreading lesions, if the cat is known to be immunosuppressed, if crusting is rapidly extending, or if the cat is also unwell in itself.

Book within the week for any scaly patch with broken hairs, any moth-eaten ear margin, any new lesion in a multi-cat household, and for any flaking that appears alongside weight loss, increased thirst or a change in appetite.

See a doctor, and mention the cat, for any new ring-shaped itchy patch on a person in the household. Children, older adults and anyone on immunosuppressive treatment should be seen promptly rather than watched.

At the appointment the vet will examine the whole coat rather than the patch you point at, may use a lamp as a first pass, will pluck hairs from the edge of a lesion for microscopy and culture or PCR, and will discuss whether other pets in the house need testing.

Bring the cat's history, the list of other animals in the home, anything you have already applied, and your photographs. In a household outbreak the history usually identifies the source faster than examining any single animal.