Rain Rot in Horses: Signs, Contagion and How It Differs from Mud Fever

Rain rot in horses: what it is and why everyone is asking

Rain rot in horses is a bacterial skin infection, caused by Dermatophilus congolensis, that shows up as crusty scabs with tufts of hair stuck in them, usually along the back and rump after a stretch of wet weather. It is contagious between horses through direct contact, shared brushes, blankets and tack, and biting insects, and it can rarely infect the hands and arms of the people who handle them.

Vets call it dermatophilosis or rain scald. The same germ is also one of several culprits behind mud fever, the sore, scabby skin on the back of the pasterns that many U.S. owners call scratches.

The name has been in the headlines since June, when the European Centre for Disease Prevention and Control (ECDC) reported 70 human cases in France, Germany, Spain and Sweden, plus cases in Norway and Austria. ECDC said those infections most likely spread from person to person through close skin contact, investigators found no contact with sick animals in the main clusters, and ECDC rated the risk to the general public as very low.

For horse owners, the bigger story is the weather. Across much of Mexico and Central America, September is still rainy season, and in the U.S., fall brings wet turnout and incoming winter coats. Moisture is exactly what this bacterium needs, and long hair hides scabs until you run a hand over the horse.

How to spot rain rot: the hands-on check

Rain rot is often easier to feel than to see. Run a flat palm along the neck, withers, back, loins and rump, then down each leg, feeling for small raised bumps; Penn State Extension recommends this kind of hands-on check in winter, when a long coat hides lesions.

Classic signs of rain rot:

• Small tufts of matted hair that stick up like the tip of a paintbrush
• Raised crusts or scabs with hair stuck in them, often in clusters
• Bald, pink or raw patches where scabs have come away, sometimes with yellow-green pus under larger scabs
• Soreness when you touch or brush the area; itching varies from horse to horse
• Lesions on the topline, rump, face or legs, and on white-skinned areas of the lips and nose

Which horses get it most?

• Horses turned out without shelter through days of rain or high humidity
• Young and senior horses, and any horse with a weakened immune system
• Horses with lighter coats or white-skinned patches
• Horses whose skin is already rubbed or scraped, including under ill-fitting tack or a damp blanket
• Barns with lots of flies or ticks, which can carry the bacteria from horse to horse

A horse can carry the bacteria without looking sick. According to the Merck Veterinary Manual, chronically infected animals that look normal are the main reservoir, and outbreaks occur on farms that have had affected horses before.

Our grooming guide shows how to build this into a daily check.

Is rain rot contagious to other horses and people?

Yes, with a catch. The bacteria spread through direct contact, contaminated gear and surroundings, and possibly biting insects, but Merck notes infection takes hold mainly when the skin's defenses are down. A horse with dry, healthy skin can often shrug off exposure, while a soaked or scraped one is primed for it.

People can catch it too, though it's uncommon. Merck says direct contact with an infected horse can cause infections on the hands and arms, and ECDC notes human cases have historically been rare and usually tied to animal exposure, so wear gloves on scabby skin and wash your hands and forearms afterward.

The reverse worry, people passing it to horses or pets, has not been documented, according to ECDC. As a precaution, ECDC still advises anyone with skin lesions to avoid close contact with pets and livestock.

Stop-the-spread checklist:

• Give the affected horse its own brushes, saddle pad, girth and blanket until the skin heals
• Groom healthy horses first and the affected horse last
• Bag scabs and loose hair and put them in the trash instead of leaving them in the aisle
• Clean and disinfect brushes, pads and blankets before another horse uses them, and replace tools you can't clean
• Wear gloves, then wash your hands and arms with soap
• Keep up fly and tick control while insects are still active

Rain rot vs scratches (mud fever): how to tell them apart

The quickest clue is location. Rain rot mostly shows up on the back and rump, where rain soaks the coat, while mud fever lives on the lower legs, especially the back of the pastern and the heel bulbs.

Mud fever is a syndrome, not a single germ

Mud fever's proper name is pastern dermatitis, and it also goes by scratches, greasy heel and cracked heels. It is a pattern of skin damage on the lower leg with several possible triggers:

• Bacteria, including the same Dermatophilus behind rain rot; Merck notes white legs are hit harder
• Fungal infections
• Chorioptic mites (leg or feather mange), most common in horses with long, feathered legs
• Pastern vasculitis, an immune reaction that targets white legs, tends to worsen with sunlight and may lead your vet to check liver function

That's why a cream that "fixed" one horse fails on another. A correct diagnosis from your vet saves time and money.

Signs of mud fever

• Matted hair over crusty scabs, with small, moist, round sores underneath
• Creamy white, yellow or greenish discharge between the skin and the scab
• Horizontal cracks at the back of the pastern, which is where "cracked heels" comes from
• Heat, swelling and pain when the leg is pressed or bent, and lameness in bad cases

Not sure where the pastern and fetlock are? See our anatomy guide.

Gentle scab care: no scrubbing, no picking

Plenty of barn advice still says to scrub scabs off. That hurts, and University of Minnesota Extension notes picking seems to make scratches swell more. The steps below are hygiene and comfort basics; your vet decides on any medicated wash, cream or antibiotic.

1. Call your vet if patches are widespread, weeping or on a sore leg, or you're not sure what you're looking at. Ask which wash to use and how to lift the scabs.
2. Get the horse out of the wet. Shelter, a dry stall or a dry lot matters more than any product.
3. Put on gloves and use the horse's own brushes.
4. Soften, don't pick. Crusts should be softened until they lift easily, following your vet's instructions. Never tear dry scabs off; they're anchored to hair roots over raw skin.
5. Go easy on washing. UMN advises washing affected legs no more than once a day and avoiding repeated harsh cleansers or disinfectants, since constant moisture irritates delicate skin.
6. Dry completely. Blot with a clean towel or paper towels; Horse & Hound's vet-approved guide suggests a hair dryer if your horse accepts it.
7. Only use barrier creams on clean, dry skin. A greasy layer over wet, infected skin can trap bacteria underneath.
8. Bag the scabs and clean your tools when you finish.

How long does it take to heal?

Most rain rot clears in two to three weeks once the skin stays dry, and it usually heals without scars, according to the Merck Veterinary Manual. Dry weather speeds things up.

Mud fever can be more stubborn. Severe cases can take many weeks, and damaged skin may stay prone to flare-ups.

Antibiotics aren't automatic: not all mud fever is bacterial, and vets increasingly save them for cases that truly need them.

Keeping backs and legs dry: blankets, turnout and mud

Blankets and sheets

A blanket can help or hurt. A waterproof, breathable turnout sheet keeps rain off the back, but one put on a wet horse, or one so heavy the horse sweats, keeps the skin warm and damp; Horse & Hound's vet-approved guide notes that constant wetting and sweating weaken the skin's defenses.

• Only blanket a dry horse, and check for sweat behind the elbows and along the edges
• Slide a hand under the blanket daily and take it off regularly to look at the skin
• Don't share blankets or saddle pads between horses, and wash one that covered rain rot before reusing it
• If your horse already has rain rot, ask your vet whether to blanket during treatment

Our care guide and tack and equipment guide cover the basics.

Legs, mud and bedding

• Don't hose legs after every ride without a reason, and dry pasterns completely when you do
• Keep bedding clean, dry and non-irritating
• Rotate paddocks, fence off churned-up gateways, and add gravel or a firm base where horses gather
• Put turnout boots or wraps only on clean, dry legs, and make sure they don't rub
• Clean boots, wraps and hobbles before using them again

Should you clip leg feathers?

It depends. UMN recommends clipping long hair from affected skin so it's easier to clean and dry, but Horse & Hound's vet-approved guide notes feathers can act as a protective, water-shedding layer unless they're soaked or full of mites. Close clipping can also expose delicate skin, so talk to your vet before clipping a draft or cob.

When to call the vet, and what to watch this fall

Call your vet if you see:

• A hot, swollen or painful leg, or any lameness
• Scabs spreading over large areas, or a horse that's dull or off its feed
• Sores that aren't improving with clean, dry care
• Lesions only on white legs, especially if they creep up the cannon bones
• Skin problems in a foal, a senior or a horse with other health issues
• A rash on your own hands or arms after handling the horse (see your doctor too)

Your vet may check a scab under a microscope, or take a skin biopsy in stubborn cases. Our health basics page covers the vital signs to note before you call.

What to watch next:

• Long wet spells: do a hands-on topline check after every few days of rain
• Blanket season: check under every sheet and blanket, especially after mild, damp days
• Muddy gateways and water troughs: fix drainage now, before winter freeze-thaw churns them up
• The European story: ECDC asked countries to keep investigating the human clusters; for owners, gloves and handwashing remain the takeaway