Cat Scratching and Crusty Sores: Fleas, Food or Eosinophilic

A cat that licks itself raw, or one whose spine is covered in tiny scabs you can feel but barely see, does not have a grooming problem. Itch in cats runs on four engines — fleas, food, environmental allergens and infection — and where the lesions sit narrows that list faster than any blood test.

See a vet the same day if a sore is weeping pus, the chin or lips are swollen and painful, the cat has stopped eating, or itching began within hours of a new flea product or drug.

Where the lesions are is the fastest clue

Distribution	Most likely cause	What confirms it
Tail base, lower back, back of thighs	Flea allergy dermatitis	Flea comb, visible flea dirt
Head, ears, chin, neck	Food allergy or ear mites	8-week elimination diet
Belly, chest, inner legs, face	Environmental allergy	Seasonal pattern
Dense 1 to 3 mm scabs on the spine	Miliary dermatitis	Scrape plus cytology
Lip margin ulcer, pink plaque on thigh	Eosinophilic granuloma complex	Biopsy
Ring-shaped scaly patch, broken hairs	Ringworm	Fungal culture, 10 to 14 days

Miliary dermatitis: the scab pattern

Miliary means millet-seed sized, and that is how it feels: 1 to 3 mm crusts packed along the spine, usually with a dull greasy coat and dandruff. It is a reaction pattern, not a disease, and in cats it is the most common way an allergy shows up. Owners describe a ripple running down the back when the cat is touched. Under the microscope most of these scabs are self-trauma plus secondary bacteria or yeast, and a scrape with cytology takes 10 minutes to tell you which. Antibiotics alone clear the crusts for 2 weeks and then the cat is back.

Eosinophilic granuloma complex

Three conditions share one name. The indolent ulcer is a raised, red-brown, painless sore at the upper lip margin that can sit unchanged for months. The eosinophilic plaque is a raised, pink, ulcerated, very itchy lesion on the thigh, belly or face. The granuloma is a firm nodule on the chin or behind a thigh, sometimes a linear streak down a leg. None is cancer, but they look like it, and biopsy is often the only way to be sure. They respond to glucocorticoids, commonly triamcinolone at 0.1 to 0.2 mg per kg daily tapered over 3 to 4 weeks, and they return within weeks if the trigger is never found.

Food allergy hides on the head and neck

Food allergy is less common than flea allergy and more common than most owners assume. Its signature is itch concentrated on the head, face, ears, chin and neck, often with repeated ear infections or a swollen chin, and often year-round. Gut signs are optional: perhaps 20 to 30 percent of these cats also vomit or pass soft stool. The only reliable test is an 8-week elimination trial on a hydrolysed or novel-protein diet, fed exclusively — no treats, no table food, no flavoured toothpaste, no other cat's bowl, no hunting. Most improve in 4 to 6 weeks.

The three-step rule-out, in order

The sequence matters because each step is ruined by skipping the one before it.

1. Fleas, 8 weeks, every animal. Treat all cats and dogs in the house monthly with an adulticide for at least 8 weeks, vacuum daily for the first 2, and do not judge by visibility — an allergic cat often carries fewer than 5 fleas.
2. Food, 8 weeks, exclusive. Hydrolysed or novel protein with no exceptions, scoring itch from 1 to 10 daily so the change is measured rather than remembered.
3. Environment, 4 to 8 weeks. HEPA filter in the bedroom, dust-free litter, no scented plugins, bedding washed weekly at 60 degrees.

Only after all three fail is a cat a candidate for lifelong control with ciclosporin, oclacitinib where licensed, or allergen immunotherapy.

Ringworm has to be checked at the same time

Not every scaly cat itches, and not every itchy bald patch is an allergy. Ringworm (usually Microsporum canis) gives circular patches with broken hairs and scale, sometimes almost no itch, and it is contagious to people. A Wood's lamp is suggestive but misses cases; fungal culture takes 10 to 14 days and is the standard. Steroids on a ringworm cat make the lesion explode. Any patchy hair loss gets a scrape for mites plus a culture before the first steroid tablet.

What actually stops the itch

Short term: a glucocorticoid burst, essential fatty acids at 20 to 40 mg per kg of EPA and DHA daily, a 2 percent chlorhexidine shampoo every 3 days for 2 weeks, and a collar to break the lick cycle. Never use human hydrocortisone cream on a cat's face or anywhere it can lick. Long term the answer is the trigger, not the drug: cats kept on permanent steroids for itchy skin collect diabetes, thin skin and recurrent bladder infections within 2 to 3 years.

Five steps for this week

1. Photograph each lesion beside a coin, with the date.
2. Start flea control for every animal today and set an 8-week reminder.
3. Book a scrape and cytology before any steroid; add a culture if there is hair loss.
4. Keep a nightly itch score from 1 to 10.
5. If fleas are cleared and itch persists, start the diet trial and stop all treats the same day.

Doing flea control properly is covered in fleas and worms, the mechanics of changing food without diarrhea in how to switch cat food, and cutting dust and scent at home in cat-proofing your home.

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