Where the coat is thin tells you more than what the skin looks like. Before any test, split the body into 5 zones and note which ones are bare, because the zone combination narrows the cause to a short list. Then measure the largest bare patch in centimeters and repeat every 14 days: a patch that has not changed in 42 days is not seasonal shedding, whatever the calendar says.
Why zone beats appearance
Most owners describe hair loss as patchy or uneven, which fits nearly every cause. Zones do not. Symmetrical thinning on both flanks and the belly, with an intact coat on the head, points at hormones or over-grooming. Loss on the ears, chin, and neck edges points at parasites or fungal infection. Loss on the lower back and tail base is the classic flea area. Each of those 3 patterns has a different first test and a different 2-week action, so the zone map saves a round of guessing and 1 or 2 unnecessary visits.
The 5 zones and what each one tells you
| Zone | Landmark | Pattern commonly seen | Bare width (cm) | Score 0-3 | Recheck |
|---|---|---|---|---|---|
| 1 Ears and head | Ear base to crown | Crusts, thinning at edges | 0 to 4 | 0-3 | Day 14 |
| 2 Chin and neck | Under jaw, throat fold | Round patches, scale | 0 to 3 | 0-3 | Day 14 |
| 3 Flanks and belly | Last rib to groin | Symmetric, barbered | 0 to 8 | 0-3 | Day 14 |
| 4 Lower back and tail base | Withers to tail root | Scabs, flea dirt, stud tail | 0 to 6 | 0-3 | Day 14 |
| 5 Legs and paws | Inner thigh, wrist | Linear streaks, swelling | 0 to 3 | 0-3 | Day 14 |
Score each zone 0 for full coat, 1 for thin but covered, 2 for visible skin, 3 for bare with crusts or sores. A total of 0 to 2 is normal variation; 3 to 5 needs the 14-day log; 6 or more, or any single zone at 3, means book a visit now. Write the score on the same sheet as the centimeter measurement, because a patch can score lower while spreading.
Normal shedding versus a problem
Cats shed heavily 2 times a year, for 2 to 4 weeks each, and lose 20 to 30 percent of coat volume without bare skin. Regrowth starts within 6 to 8 weeks and the coat looks even. A problem looks different: a bare patch that grows more than 1 cm in 7 days, skin that stays bare past 42 days, or hair that comes out in tufts when you stroke the back 3 times.
Pattern 1: symmetrical, both sides alike
Thinning that mirrors itself across the spine, usually flanks and belly, is rarely infectious. Common causes are over-grooming, chronic itch, and in older cats an endocrine problem. Weigh the cat: a 10 percent weight loss over 8 weeks with a good appetite and a scruffy coat is a reason to ask for blood work, not a new shampoo. Symmetry also appears after 6 to 8 weeks of stress grooming, so ask whether the cat licks for more than 5 minutes at a time.
Pattern 2: round patches with scale
Round, scaly patches on the head, ears, or front legs suggest fungal infection. A Wood lamp glows in fewer than 50 percent of cases, so a negative lamp proves nothing and a culture takes 10 to 21 days. In a multi-cat home, isolate the cat and wash bedding at 60 C. Ringworm is contagious to people, so check your own forearms for a ring 2 to 3 weeks after handling.
Pattern 3: barbered streaks and scabs
Coat clipped to 1 or 2 mm in lines, with intact skin and no scale, is self-inflicted. Look along the inner thighs and the belly, then look for a cause: fleas, food allergy, arthritis in the hips, or a painful tooth. Flea comb the lower back 10 strokes over white paper; dampen the debris, and a red-brown smear means flea dirt. Treat the whole household for at least 3 months, not just the itchy cat.
The 2-week record that answers the question
Photograph all 5 zones on day 1, day 14, and day 28, from the same distance of 40 cm, in the same room light, with a ruler laid beside the largest patch. Note 4 things per entry: zone score, patch width in mm, new scabs yes or no, and itching bouts counted in 10-minute windows. Bring the sheet to the visit. A vet who can see 3 dated photos and a 14-day trend skips the trial-and-error shampoo and goes straight to a skin scrape or a diet trial.
When to stop watching and go in
Book within 24 hours for spreading redness, pus, a patch over 5 cm, or a cat that stops eating. Book within 3 days for weight loss over 10 percent, scabs that bleed, or hair loss that reached a second zone inside 14 days. Deep skin infections and ear margin crusting in an older cat are not wait-and-see problems.
What the first visit usually costs
A skin scrape runs 40 to 120 USD, a fungal culture 30 to 80 USD, a blood panel 80 to 200 USD, and a 8-week hypoallergenic diet trial 60 to 140 USD. Doing the 14-day log first often removes 1 of those 4 from the bill, and it makes the remaining tests easier to justify.
Start the log tonight
- Part the coat along the spine and both flanks with a comb, not your hand.
- Photograph 5 zones at 40 cm with a ruler in frame, and label the date.
- Score each zone 0 to 3 and write the total on the calendar.
- Repeat on day 14 and day 28 before changing food, shampoo, or litter.
If the cat is also overweight, the extra weight changes grooming reach and skin folds, so pair this log with the weight-loss plan and plot both on the weight trend chart. Any exposure to a household product or plant belongs on the toxin list before you treat the skin.
Terms mentioned in this article
Frequently asked
Is symmetrical hair loss on the flanks always hormonal?
No, and that is the most expensive assumption owners make. Symmetry fits over-grooming and chronic itch just as well, especially when the coat is clipped to 1 or 2 mm and the skin underneath looks healthy. Blood work is reasonable after 42 days without regrowth, but a 14-day itch count and a flea check come first and cost far less.
How fast should a bare patch regrow?
New coat usually appears at the edges within 6 to 8 weeks once the cause is gone, and full coverage takes 3 to 4 months because cat hair grows in cycles. Measure the patch every 14 days; if the width has not shrunk by 10 percent in 28 days, the cause is still active or the diagnosis was wrong.
Can I just use an over-the-counter antifungal shampoo?
It hides the evidence and delays a culture. Many shampoos also dry the skin, which adds scale and makes the next exam harder to read. Bathe only after a diagnosis, use the contact time printed on the bottle, and treat every cat in the home, since carriers show no patches at all.