Skin / coat abnormalities

Does your cat have bald patches, a rash, or scabs on the skin?

This is about visible skin lesions — bald patches, rashes, scabs, broken skin — not simply "grooming more" (that falls under the "overgrooming" category). Here, the skin itself already shows an actual physical change.

Possible medical causes

Flea allergy dermatitis: an allergy to flea saliva, one of the most common causes of skin problems in cats
Food allergy / environmental allergens: persistent itching, skin lesions, and gradually worsening coat condition — this usually doesn't happen overnight, but worsens slowly over time
Ringworm (fungal infection): classically shows as a round patch of local hair loss with a red ring around the edge. This is zoonotic — it can spread to humans too — so be especially careful if you spot it
Eosinophilic granuloma complex: usually triggered by allergies (fleas/insect bites/food), and can present as ulcers, rashes, or lumps

Possible behavioral causes

Warning signs — see a vet right away

A round bald patch with a clear red ring around the edge (possible ringworm — watch for zoonotic transmission risk)
Ulcers, lumps, or widespread rash on the skin
Hair loss that keeps spreading, or symmetrical hair loss
Combined with intense itching and skin that's broken and weeping

Initial at-home suggestions

Use a flea comb to check for fleas or black flea dirt
Observe whether hair loss is symmetrical or a local round patch — a round local patch should raise suspicion for ringworm first, so handle it carefully
If ringworm is suspected, temporarily avoid close physical contact and clean the environment to lower the risk of transmission between humans and pets
Note how quickly it changed: a lesion that appeared suddenly and one that worsened gradually indicate different levels of urgency

Sources: Cornell Feline Health Center、iCatCare. For reference only — please consult a vet.