Low severity

Rain rot (Rain scald)

Rain rot — also called rain scald — is a bacterial skin infection (Dermatophilus congolensis) that shows up on the back, croup, and rump after prolonged wet weather. Moisture softens the coat, the organism multiplies in the hair follicles, and paintbrush-like scabs form. A photograph cannot diagnose rain rot, and the app scan is a first look at the skin, not a verdict that your horse has rain rot.

Symptoms to watch for

Matted tufts of hair on the back, croup, or rump that lift as paintbrush-like scabs

Scabs with a concave underside and a small patch of raw or pink skin beneath

A dull, staring coat along the topline after days of rain

Tenderness when grooming the back or quarters

Lesions that follow the drip line of a wet rug or an uncovered back

In more advanced cases, larger crusted patches or secondary infection — many horses stay bright and eat normally

Common causes

Prolonged wet weather that keeps the back and croup soaked
A damp rug or wet coat that never fully dries between turnout and stabling
Dermatophilus congolensis — the same organism often involved in mud fever — taking hold in softened skin
Shared grooming kit, rugs, or brushes that move scabs from horse to horse
A thick or dirty winter coat that traps moisture against the skin
Minor skin damage from rubbing, insects, or poorly fitting rugs

Prevention

Keep the back and croup dry — a well-fitted waterproof rug in wet weather, and shelter so the coat can dry
Towel or air-dry a soaked topline rather than leaving a wet rug or wet coat overnight
Do not share brushes, curry combs, or rugs between an affected horse and the rest of the yard
Groom only when the coat is dry; wet brushing drives moisture into the follicles
Wash and dry rugs so the lining is not a damp, dirty layer against the back
Do not treat a photo or a scan result as a diagnosis

What to do

1
Move the horse onto dry standing and keep the back and croup dry. Rain rot will not settle while the coat stays wet.
2
Leave dry scabs in place. Do not pick or peel them — picking opens skin, hurts, and can spread the organism.
3
If a vet or the label of a recommended wash directs it, soften crusts with a mild antibacterial wash and lift only what comes away easily, then pat the area dry.
4
Keep the horse dry between treatments. A clean, dry rug can help once the coat is dry; a wet or dirty rug will undo the work.
5
Wash grooming tools and rugs used on the affected horse so you do not carry the infection to another horse.
6
If the horse is dull, off feed, feverish, or the patches are spreading, painful, or weeping, stop home treatment and call the vet.

When to call the vet

Pick up the phone if…

Call the vet if the horse is dull, off feed, or has a fever; if lesions are widespread, painful, or weeping; if the infection is on the face or over joints; or if keeping the horse dry for one to two weeks has not improved the scabs. Rain rot can be confused with ringworm, sweet itch, lice, or a photosensitivity rash — those need a vet, not a photo guess.