Emergency

Cellulitis

Cellulitis is a bacterial infection of the tissues under the skin — typically a sudden, hot, painful swelling of one limb, often a hind leg. It is an emergency-leaning limb infection, not a rash, and not melanoma, ringworm, or sarcoid. A photograph cannot diagnose cellulitis. Diagnosis is a vet exam. The skin scan is a first look at the swollen limb, not a verdict that your horse has cellulitis, and there is no cellulitis scanner.

Symptoms to watch for

Sudden, hot, painful swelling of one limb — often a hind leg

Skin that is tight, shiny, or pits when pressed

Reluctance to bear weight, or a short painful stride on that limb

Heat in the limb, and sometimes a fever or a dull, off-feed horse

A small wound, cracked heel, or scab that may have been the entry — or no obvious wound

Swelling that can climb the limb quickly; a change in size or heat is a reason to call the vet, not a photo verdict

Common causes

Bacteria entering through a small wound, cracked heel, mud-fever scab, or insect bite
A sudden swollen limb after wet, muddy standing or a knock — location is a clue, not a diagnosis
Infection in the subcutaneous tissue that the lymphatics cannot clear
A limb that has swollen before and is more likely to swell again
Not a rash (hives), not melanoma (a pigment-cell tumour), not ringworm (fungal), and not sarcoid (a BPV tumour) — those can look different and still need a vet

Prevention

Watch for sudden one-limb swelling, heat, or a horse that will not bear weight, and call the vet rather than waiting for a photo guess
Keep small wounds, cracked heels, and mud-fever scabs clean and dry
Do not wait to see if a hot, painful swollen limb goes down overnight
Do not treat a photo, a swollen limb, or a scan result as a diagnosis
Skin photos can help you and your vet track a swollen limb over time — they do not confirm or rule out cellulitis

What to do

1
Call the vet for a sudden hot, painful swollen limb. Diagnosis is a vet exam, not a photograph.
2
Photograph the limb in good light and keep it on the horse's record so you and the vet can see change over time.
3
Do not ride, do not give pain medication unless your vet directs it, and do not start antibiotics from a photo guess.
4
Use a skin scan only as a first look at the swollen limb to share, not as a cellulitis test. There is no cellulitis scanner.
5
If cellulitis is confirmed, follow the plan your vet prescribes — that may include antibiotics, anti-inflammatories, cold hosing, or stall rest. 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.

⚠ Emergency · call your vet now

Do not wait.

Call the vet now if one limb is suddenly hot, painful, and swollen, if the horse will not bear weight, is dull or off feed, or has a fever. Do not wait to see if it settles. A photograph cannot diagnose cellulitis. Diagnosis is a vet exam. Cellulitis is an emergency-leaning limb infection — not a rash, not melanoma, not ringworm, and not sarcoid. The skin scan is a first look at the swollen limb, not a verdict, and there is no cellulitis scanner.