High severity

Anhidrosis (Non-sweating)

Anhidrosis is decreased or absent sweating (non-sweating), often in hot or humid climates — a dry coat when other horses are wet after work, with rapid breathing, high temperature, fatigue, or heat stress. It is not photosensitivity (a sun/skin reaction), not hives (raised wheals), and not sweet itch (Culicoides). A photograph cannot diagnose anhidrosis. A still cannot tell anhidrosis from a horse that has not worked, is clipped, is dehydrated, or is just dry. Diagnosis is a vet exam. The skin scan is a first look at the coat/skin to share with a vet, not an anhidrosis test, and there is no anhidrosis scanner.

Symptoms to watch for

Dry coat when other horses are wet after work — the dry coat is a clue, not a still-photo verdict

Rapid breathing or a high temperature after work in heat or humidity — a reason to book a vet, not a photo verdict

Fatigue or heat stress when the work should be ordinary — a clue, not a diagnosis

Decreased or absent sweat on the neck, flanks, or under the saddle — location is a clue, not a diagnosis

A dry coat that can look like a horse that has not worked, is clipped, is dehydrated, or is just dry — a still cannot tell them apart

A still photo is especially weak here: a dry coat is not a lesion you can point at — a reason to book a vet, not a photo verdict

Common causes

Decreased or absent sweating (anhidrosis / non-sweating), often in hot or humid climates — the climate and the dry coat after work are clues, not a diagnosis
Not photosensitivity (a photodynamic / sun / skin reaction), not hives (urticaria — raised wheals), and not sweet itch (Culicoides insect-bite hypersensitivity)
A still cannot tell anhidrosis from a horse that has not worked, is clipped, is dehydrated, or is just dry — those need a vet
Heat stress and overheating can follow when the horse cannot cool by sweating — that is a vet visit, not a photo

Prevention

Watch for a dry coat when other horses are wet after work in heat or humidity, and book a vet rather than waiting on a photo
Do not work through a dry coat, rapid breathing, or a high temperature hoping it will settle — that is a vet visit, not a photo (overheating risk)
Note heat, humidity, work, clipping, and water intake so you can tell the vet
Do not treat a photo, a dry coat, or a scan result as a diagnosis
Skin photos can help you and the vet look at the coat and skin — they do not confirm or rule out anhidrosis, and they cannot tell it from a horse that has not worked, is clipped, is dehydrated, or is just dry

What to do

1
Book a vet visit if the horse stays dry when other horses are wet after work, or is breathing hard, running a high temperature, or showing fatigue or heat stress. Diagnosis is a vet exam — not a photograph.
2
Stop work in heat. Cool the horse and do not ride through a dry coat, rapid breathing, or a high temperature hoping it will settle.
3
Photograph the coat in good light, after work if it is safe, and keep the photos on the horse's record so you and the vet can see change over time — a first look to share, not a diagnosis.
4
Use a skin scan only as a first look at the coat/skin to share, not as an anhidrosis test. There is no anhidrosis scanner.
5
If anhidrosis (non-sweating) is confirmed, follow the plan your vet prescribes. Do not start a treatment protocol from a photo.
6
Keep the vet on the same page. Share what you see; do not treat a photo as a verdict.

When to call the vet

Pick up the phone if…

Schedule a vet visit if the horse stays dry when other horses are wet after work, or is breathing hard, running a high temperature, or showing fatigue or heat stress. Call sooner if the horse is dull, off feed, collapsing, or you cannot cool them — overheating is a vet call, not a photo diagnosis. A photograph cannot diagnose anhidrosis. A still cannot tell anhidrosis from a horse that has not worked, is clipped, is dehydrated, or is just dry. Diagnosis is a vet exam. The skin scan is a first look at the coat/skin, not an anhidrosis test, and there is no anhidrosis scanner.

Get a first look at the coat

Scan the skin in HorseCare. 5 free scans this month, then Pro.

Scan the skin

5 free scans this month, then Pro. Scans run in the HorseCare app.

Educational content only. Not a substitute for veterinary advice.