Rain rot in horses (rain scald): what it looks like, whether it spreads and how it heals

What is rain rot in horses?

Equine rain rot is a bacterial skin infection: Dermatophilus congolensis normally lives quietly on the skin and invades when the skin's own defenses break down, usually because the coat has been wet for a long time. Dr. Leslie Easterwood of Texas A&M described it in 2021 as an organism that is "a normal inhabitant of the skin but may invade the skin when the skin's normal defenses are compromised". Merck calls it an actinomycete, an organism that resembles bacteria and fungi, and the other sources simply call it a bacterium; it is not a fungus. In the UK the same condition is called rain scald, and the British Horse Society notes it is often diagnosed in the autumn or winter months because horses are out in wet and muddy conditions for weeks on end.

What causes rain rot in horses?

Rain rot is caused by Dermatophilus congolensis getting into skin that has been softened by prolonged rain, high humidity or sweat, or damaged by mud and biting insects. The Merck Veterinary Manual says the organism "can live in the skin quietly until infection is stimulated by climatic conditions", and that prolonged wetting by rain, high humidity and high temperature all increase how often it occurs. Penn State Extension adds increased exposure to biting insects and warns that caked mud can compromise the skin. Merck's veterinary chapter explains why flies matter: humid weather brings more biting insects, particularly flies and ticks, which act as mechanical carriers of the bacterium.

So how do horses get rain rot in the first place? Merck's veterinary chapter says that animals which carry the infection without showing it are considered the primary reservoir, that outbreaks occur on farms with previously affected horses, and that attempts to find the bacterium living in soil have failed. In other words, the rain is the trigger rather than the source: the bacterium can already be on the farm, sometimes on a horse that looks perfectly healthy.

What does rain rot look like on a horse?

Rain rot looks like small, raised scabs that hold clumps of hair, so the hair comes away in tufts with the scab and leaves a bald, sometimes raw patch underneath. Penn State describes small patches of raised bumps that are scabs containing clusters of hair. The British Horse Society calls them scabs coming off with tufts of hair that look like little paintbrushes, and Merck's veterinary chapter uses the same word for the "paintbrush" lesion, where the base of each tuft sits in a thick crust of dried serous exudate. Texas A&M describes thick crusts that give the skin a bumpy feel.

The coat changes the picture. In a long winter coat, Merck says the hair mats and the scabs can have yellow-green pus underneath; in a short summer coat, matting and scabs are uncommon. On where it appears, Penn State says it is most often found on the horse's topline but can also appear on the rump, face and legs, and the BHS names the neck, back and hindquarters.

Does rain rot itch? The sources differ in emphasis. Penn State says the scabs "do not typically itch but can be painful", while Merck writes "Itching is variable." and adds that some wounds may be painful.

Early stage rain rot

In a long winter coat, early stage rain rot can be easier to feel than to see: small, hard bumps under the coat, usually along the back. Penn State notes that hands-on palpation may be needed, particularly during winter months, because a long coat makes it hard to judge by eye. The BHS calls thoroughly inspecting the skin to identify early signs of rain scald an important part of prevention. In practice, that means feeling the coat with your hands as well as looking at it, especially in winter.

Rain rot on the legs and face

Rain rot on a horse's legs and face is most likely on white legs and on the white, pink-skinned parts of the lips and nose, and on the lower legs it overlaps with scratches, also called mud fever. Merck's veterinary chapter says that persistently wet pasterns lead to lower limb infection and that white legs and the white-skinned areas of the lips and nose are more severely affected. Scabs on the lower legs are not automatically rain rot, though. In a 2018 study using PCR, Dermatophilus congolensis was found in only 1 of 15 horses with pastern dermatitis, and the authors concluded that it "was uncommonly associated with pastern dermatitis in horses in this population." A 2023 review describes it as infrequently identified or not at all in those cases. Our guide to scratches and mud fever covers the lower legs and the signs there that need a vet.

Rain rot or something else?

Rain rot can look like ringworm, which matters because ringworm is a highly contagious fungal infection that also spreads to people, so the BHS and Blue Cross both want a vet to rule it out. The BHS says it is important to confirm the signs are not mistaken for other skin conditions such as ringworm. Blue Cross, in advice reviewed in 2023, says "Ringworm is highly contagious to other horses and people" and that it starts as tufts of raised hair that fall off and leave weeping wounds. Merck's veterinary chapter lists ringworm and an immune-mediated scaling disease, pemphigus foliaceus, among the conditions to tell it apart from.

Itch is a useful clue for the other usual suspects. Blue Cross describes sweet itch as an allergic reaction to the saliva of midge and mosquito bites, seen between March and November, and says that mites and lice are a common cause of itching. If itching is the main sign, our guide on flies and sweet itch covers the summer itch that Blue Cross describes.

Is rain rot contagious?

Whether rain rot is contagious depends on whom you ask: Merck and the Penn State and Arkansas extension services treat it as spreading by contact and shared kit, and Merck and Arkansas also by insects, while the British Horse Society and Blue Cross call rain scald non-contagious. Merck's veterinary chapter says it is believed to spread by direct contact between animals, through contaminated environments, or possibly via biting insects, and Merck's owner pages advise isolating infected horses and keeping tack, blankets, grooming tools and other accessories clean. Penn State suggests you may want to keep horses with rain rot separated from others and to disinfect and replace contaminated grooming tools and other equipment as needed. On the other side, the BHS writes "Rain scald is a non-contagious skin condition", and Blue Cross (2023) says "Like mud fever, it is non-contagious".

The disagreement is smaller than it looks. Merck's veterinary chapter says dermatophilosis is "contagious only in that any decrease in systemic or local skin resistance favors establishment of infection and subsequent disease." In plain terms, the bacterium can be carried from one horse to the next, but it only takes hold on skin that is already soaked or damaged. And the same BHS page that calls it non-contagious also warns that the bacteria in the scabs can cause re-infection, so grooming kit and tack should be disinfected.

Our view: you don't need to settle the argument to do the right thing. The habits below come from the sources that treat it as spreading, and the BHS asks for clean kit too:

1. Don't share brushes, tack or rugs with other horses while you suspect rain rot (Arkansas), and disinfect contaminated grooming tools and equipment, and replace them as needed (Penn State); the BHS also asks for grooming kit and tack to be disinfected.
2. Put scabs you remove in a bag in the trash (Merck).
3. Wear gloves when you handle the affected skin, and wash your hands thoroughly afterward (Merck, Arkansas).
4. Keep flies down, because insects can carry the disease (Merck).

Can humans get rain rot?

Yes, people can catch dermatophilosis from an infected horse, on the hands and arms according to Merck, but it is rare. Merck's veterinary chapter says that direct contact with an infected animal can lead to infections on the hands and arms, recommends handling affected animals with gloves and washing thoroughly with an antimicrobial soap, and notes that "The few human cases reported have typically been associated with handling diseased animals." The British Equine Veterinary Association lists Dermatophilus congolensis, "rain scald / mud fever", among the notable pathogens that can pass from horses to people, while stressing that confirmed horse-to-human infections are relatively rare. One published case, from 2007, describes a 15-year-old girl with pustular skin infection who had just returned from horseback riding camp. The BHS takes the opposite view and says rain scald doesn't spread from one horse to another or to people.

Which horses get rain rot?

Rain rot is most common in horses that stay wet for long periods, in young horses and in horses with a weakened immune system, including horses with Cushing's disease. Merck says it is most common in the young, in animals continually exposed to moisture and in animals with weakened immune systems. Penn State adds horses with lighter coat colors and young or older horses, without naming the study behind it, while Merck's veterinary chapter, which covers all animal species, says that age, sex and breed do not seem to affect susceptibility. Read that as: young and run-down horses get it more often, and no breed is known to be especially prone.

The BHS says horses with reduced immune function, such as those with Cushing's Disease, are particularly susceptible to skin infections, and that treating an underlying condition can reduce the risk. If you have an older horse with a coat that won't shed, our guide to Cushing's disease in horses explains the link.

Can a rug cause rain rot?

A rug can contribute to rain rot when it leaks, doesn't breathe or is too warm, because the skin underneath stays wet from rain or sweat. Blue Cross (2023) describes leaking or non-breathable turnout rugs that cause poor air circulation, so the horse's back can become constantly wet. Texas A&M says "a blanket can also create a hot, cozy environment for D. congolensis to germinate", and the BHS warns that over-rugged horses can become sweaty, and advises removing or reducing rugs on mild days. The same BHS page also says a rug can protect a horse with a thin coat, a full clip or too little weight. So a rug is not the problem in itself; what the sources warn about is a rug that leaks, doesn't breathe or makes the horse sweat. Our guide to rugs and the weather helps you set rules for which rug goes on when.

How to treat rain rot in horses

Rain rot treatment for horses starts with getting the horse out of the wet, then softening and gently removing the scabs, washing the area with an antimicrobial wash your vet recommends and keeping the skin dry until it heals. Merck is clear that "Successful treatment requires removing the horse from the damp or wet environment that triggered the infection." The BHS says the same for rain scald treatment in the UK: the horse should come out of the muddy, wet conditions, so you may need to provide adequate shelter or stabling. We name no products or strengths here on purpose; your vet chooses those for your horse.

What you can do while it heals

While rain rot heals, the sources advise keeping your horse dry, softening the scabs before lifting them off, cleaning and drying the area, and keeping his kit clean. If you're wondering how to get rid of rain rot in horses, these are the steps the sources describe, each with its source:

1. Keep him dry. Penn State advises you to keep your horse dry and reduce exposure to the conditions that set it off during treatment.
2. Soften the scabs first. Merck says the lesions should be gently soaked and scabs removed, and that your vet can give you instructions. Penn State notes that softening first makes removal easier and more comfortable. The BHS warns that removing the scabs can be painful, and that sedation may be needed.
3. Wash and dry. Penn State says a bath with an anti-microbial soap can help remove the scabs and disrupt the bacteria, and Texas A&M says mild cases can be resolved with topical medicated shampoos. The BHS describes cleaning the area with a suitable antibacterial solution and then gently drying it, usually daily until the area has healed. Ask your vet which wash to use.
4. Clip very thick hair. The BHS says clipping away extremely thick hair can help, and Merck mentions that clipping of the hair coat may be required.
5. Bag the scabs. Merck's veterinary chapter says infective material should go in bagged garbage or via burning.
6. Kit and hands. The Arkansas sheet says not to share tack, equipment or blankets and to wash your hands thoroughly after treating an infected horse; Merck advises handling affected animals with gloves; the BHS asks for grooming kit and tack to be disinfected.

Penn State also writes that currying and brushing can help promote healing and prevent the spread, and warns in the next sentence that the area may become tender as you remove scabs, so be cautious with removal. Ask your vet whether and how to brush the affected patches.

What your vet may do

Your vet can confirm rain rot by looking at a scab under the microscope, and in severe cases may take a skin biopsy or give antibiotic injections. Merck calls microscopic examination of scabs or impression smears the most practical diagnostic test. Penn State says that in severe cases a horse may need antibiotic injections given by a veterinarian, and that skin biopsies may be needed. Blue Cross (2023) adds that your vet will first want to carry out tests to rule out contagious infections such as ringworm. Merck's veterinary chapter says treatment is recommended in horses because lesions interfere with use and are painful.

Mouthwash, apple cider vinegar and other home remedies

No study in the sources we read supports home remedies such as mouthwash, apple cider vinegar, coconut oil or essential oils for rain rot in horses, and none of the sources tested and rejected them for rain rot either. One undated University of Arkansas extension sheet says only that a brand of mouthwash "has also been said to have a positive effect on rain rot", without a study behind it and without recommending it; none of the other veterinary or university sources mentions any of these remedies for rain rot, for or against. What does have the sources behind it is less exciting: a dry horse, softened scabs, a wash your vet chose, and kit that is kept clean and not shared (Merck, Penn State, Arkansas). If you have already tried something at home, the vet notes sheet below has a place to write down what has already been done.

When to call the vet about rain rot

Call your vet as soon as you think your horse has rain rot, and certainly when the scabs are large, spreading or sore, sit under the saddle, or don't seem to be healing. The BHS advises you to speak to your vet if you think your horse has rain scald, and Penn State says it is always recommended to consult a veterinarian to determine the cause and make a treatment plan. These are the signs the sources single out:

Left alone, it can get worse. Texas A&M warns that overlooked rain rot can let bacteria penetrate the horse's skin layer and lead to more painful problems such as mud fever and even cellulitis. None of the sources we read lists fever as a sign of rain rot; if your horse seems unwell in other ways, a temperature reading gives your vet something concrete, and our guide to a horse's normal temperature shows how to take one. When you call, our guide on contacting your vet helps you have the details ready.

How long does rain rot take to heal?

Most rain rot heals in 2 to 3 weeks, without scarring, once the horse's skin is kept dry; it can drag on much longer if the coat keeps getting soaked. Merck writes that "Most infections subside in 2 to 3 weeks and the wounds heal without scarring." and that dry weather speeds healing. Texas A&M gives the same two to three weeks for most mild to moderate cases. Merck's 2019 owner page was updated in 2026, and its 2025 veterinary chapter agrees on the timing. We found no source that says how long the hair takes to grow back, so we won't guess.

Will rain rot heal on its own?

Most rain rot heals on its own within about 3 weeks, as long as the skin isn't kept soaked, and Merck still recommends treating horses because the lesions are painful. Merck's veterinary chapter says most affected animals recover spontaneously within 3 weeks if chronic maceration of the skin does not occur, in other words if the skin isn't constantly wet.

Can you ride a horse with rain rot?

You may not be able to ride a horse with rain rot under the saddle area until it has been treated, and severe rain rot can limit any use of the horse. The BHS says "If the saddle area is affected, the horse may be unable to be ridden until it's successfully treated." Penn State notes that in severe cases the horse's use may be impacted. We found no source that gives a fixed rule for riding when the scabs are elsewhere, so ask your vet. The saddle pad and girth are tack, and the Arkansas sheet says not to share tack between horses you suspect may have rain rot.

How to prevent rain rot in horses

To prevent rain rot, give your horse shelter from heavy rain, limit mud, rug for the weather without letting him sweat, groom regularly without stripping the coat's natural oils, control flies and feel his skin often. The BHS admits that "Prevention can be difficult as the UK often challenges us with difficult weather." What the sources recommend:

• Shelter. Penn State suggests keeping your horse in a barn or under shelter when heavy rain is expected, and the BHS mentions field shelters, trees and hedges.
• Less mud. Penn State says limiting access to muddy areas may be helpful.
• Rugs that fit the weather. The BHS advises removing or reducing rugs on mild days so the horse doesn't sweat, and Blue Cross (2023) warns about leaking or non-breathable rugs, as above.
• Grooming, but not too much. Penn State calls regular bathing and grooming one of the best ways to prevent rain rot. The BHS adds that field-kept horses should not be over-groomed, because that removes the naturally protective oils in their coat. Penn State is writing about hygiene in general, the BHS about horses that live out.
• Clean, dry bedding and tools. Texas A&M advises owners to thoroughly clean and dry all of your horse's bedding and grooming tools.
• Fly control. Penn State recommends best management practices based on fly species.
• Your hands. Inspect the skin thoroughly and feel under a long winter coat to find early signs (Penn State, BHS).

In autumn this overlaps with everything else that changes in the field; our guide to autumn grazing covers the rest of the season.