Finding bare skin where fur was growing last week is unsettling, and the most useful response in the moment is to observe carefully rather than treat quickly. A sudden bald patch means hairs have been lost, broken, or licked away over a short period, which is different from the gradual thinning vets expect in some older cats. Leave the brush off that area, because further friction can break more hairs and irritate skin that may already be inflamed, and spend a few minutes recording exactly what you see while the details are fresh.
Look closely at the patch and the skin underneath
Part the surrounding fur gently with your fingers in good light. Note whether the patch is round or irregular, whether the edge is crisp or fading into thin fur, and whether broken stubby hairs remain in the middle — broken hairs often mean she is licking or chewing the area herself, while cleanly empty skin suggests the hairs came out at the root. Look at the surface: smooth and pale skin reads differently from skin that is red, flaky, crusty, bumpy, or weeping. Check whether hairs at the rim pull away with the lightest touch, and search the rest of her coat for smaller patches, flea dirt at the tail base, or scabs along the back that connect this spot to a wider pattern.
Think through what changed just before it appeared
Work backwards over the last week or two. A new sleeping spot against a rough surface, a scuffle with another household cat, a collar or harness rubbing one place, or a knock during a fall can each strip fur in one localised area. So can a burst of licking driven by itch, stress after visitors or building work, or pain underneath the skin making her worry at one spot. Note any new food, new cleaning product used on bedding, or a missed flea-prevention date — not to settle on a cause yourself, but because this timeline is exactly what your vet will ask about and it is hard to reconstruct a week later.
What not to put on it while you wait
Resist the cupboard of leftover creams, oils, and antiseptics. Products meant for people or dogs can be unsafe for a cat who will lick the area within minutes, steroids or antifungal creams applied early can change how the skin looks and interfere with samples the vet may want to take, and essential oils are a genuine hazard for cats. If the patch is dirty, a brief wipe with plain water on a soft cloth is enough. Stop her reaching it only if she is actively damaging the skin — and if licking is that intense, that urgency itself is a reason to call the vet the same day rather than manage it at home.
When to book, and how urgently
A single small patch on a comfortable cat who is eating and behaving normally still deserves a vet appointment within the next few days, because ringworm, bacterial infection, and mite problems are all easier to settle early and some can spread to people and other pets. Call sooner — the same day — if the patch is spreading visibly, the skin is broken, swollen, or oozing, she is off her food, or new patches appear elsewhere. At the visit, expect the vet to examine the skin closely, possibly pluck a few hairs or take a surface sample, and ask about itch, housemates, and recent changes. Bringing dated photos that show the patch on the day you found it and any spread since, stored together in KinsLe in her Pet Passport alongside her other records, lets the vet judge speed of change at a glance instead of relying on your recollection.