Allergy in cats looks different from allergy in people. Where we sneeze and stream, cats itch. The skin is where feline allergy shows itself.

What it looks like

The four common presentations:

Itching around the head and neck. Scratching at the face and ears, often to the point of sores in front of the ears.

Symmetrical hair loss, usually along the belly, inner thighs and flanks, caused by over-grooming. The skin underneath often looks normal, because the hair is being removed rather than falling out.

Miliary dermatitis, small crusty bumps scattered along the back that you feel before you see.

Eosinophilic lesions, raised pink or yellow plaques on the belly or thighs, an ulcer on the upper lip, or a swollen lower lip.

Some cats also cough or wheeze, which is feline asthma, an allergic airway disease. Runny eyes and nose are much more likely to be cat flu than allergy.

The four causes

Fleas. The most common by a wide margin. Many cats react to flea saliva, so one or two bites cause severe itching, concentrated along the back and tail base. You will often find no fleas at all, because the cat has groomed them away.

Environmental allergens. Pollen, house dust mites, mould. Often seasonal at first and becoming year round over time.

Food. Usually a protein the cat has eaten for a long time, most often beef, fish or chicken. Food allergy in cats causes itching more often than digestive upset, which surprises most owners.

Contact. Much less common. Litter, cleaning products, plastic bowls.

How it is diagnosed

By elimination, in order.

Fleas are ruled out first, always, by treating every animal in the household properly for at least eight weeks. This step is skipped constantly and it is the reason many allergy investigations go nowhere.

Food is ruled out next, with a strict elimination diet using a novel or hydrolysed protein for eight to twelve weeks. Strict means nothing else at all: no treats, no table scraps, no flavoured medication.

What remains is environmental allergy, which is managed rather than cured.

Blood tests marketed for food allergy in cats are unreliable and cannot replace an elimination diet.

Treatment

Rigorous flea control, whatever the suspected cause. A prescription diet where food is the trigger. Anti-itch medication for environmental allergy, which is managed lifelong. Treating the secondary skin and ear infections that follow persistent scratching.

When to come in

Bald patches, scabs, constant scratching, sores around the face, or a cat that has started over-grooming. Bring the details of what the cat eats, including treats, and when flea treatment was last given.