Moderate

Hives

Hives is urticaria — an allergic skin reaction that raises sudden, flat-topped wheals (plaques) that pit when pressed. It is not cellulitis (a bacterial limb infection), not rain rot, and not ringworm. A photograph cannot diagnose hives. Diagnosis is a vet exam. The skin scan is a first look at the wheals, not a verdict that your horse has hives, and there is no hives scanner.

Symptoms to watch for

Sudden, raised, flat-topped wheals (plaques) that pit when pressed

Wheals that can appear on the neck, barrel, flanks, or anywhere the coat is thin

Itching that is inconsistent; some horses rub, some do not

Wheals that can come and go within hours

In more serious cases, swelling of the muzzle, eyelids, or sheath — a reason to call the vet, not a photo verdict

A change in size or number of wheals is a reason to book a vet, not a photo verdict

Common causes

An allergic (hypersensitivity) reaction — urticaria, not a bacterial limb infection
Insect bites, feed, drugs, plants, or something in the environment — the trigger is a clue, not a diagnosis
A sudden crop of wheals after turnout, a new feed, or a vaccination
Individual susceptibility; some horses hive more than once
Not cellulitis (a hot, painful swollen limb), not rain rot (bacterial scabs), and not ringworm (fungal) — those can look different and still need a vet

Prevention

Watch for sudden wheals, especially on the neck and barrel, and book a vet rather than waiting for a photo guess
Note new feeds, rugs, sprays, or insect exposure so you can tell the vet
Do not wait to see if facial swelling or breathing change settles overnight
Do not treat a photo, a wheal, or a scan result as a diagnosis
Skin photos can help you and your vet track the wheals over time — they do not confirm or rule out hives

What to do

1
Book a vet visit for a sudden crop of wheals. Diagnosis is a vet exam, not a photograph.
2
Photograph the wheals in good light and keep them on the horse's record so you and the vet can see change over time.
3
Do not give antihistamines or steroids unless your vet directs it, and do not start a cream from a photo guess.
4
Use a skin scan only as a first look at the wheals to share, not as a hives test. There is no hives scanner.
5
If hives (urticaria) is confirmed, follow the plan your vet prescribes — that may include finding the trigger, antihistamines, or steroids. 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 you find a sudden crop of raised wheals. Call sooner if the muzzle, eyelids, or throat are swelling, the horse is dull or off feed, or breathing changes. A photograph cannot diagnose hives. Diagnosis is a vet exam. Hives is urticaria — an allergic reaction, not cellulitis (a bacterial limb infection), not rain rot, and not ringworm. The skin scan is a first look at the wheals, not a verdict, and there is no hives scanner.