All About Rainrot in Horses

Anyone with equids probably has had at least one animal with rainrot. It is a relentless, all-too-common, crusty skin affliction.

Rainrot is an infection of the skin’s top layer, caused by a species of bacterium called Dermatophilus congolensis. This microorganism normally lives dormant in the skin until awakened by a compromising of the skin’s natural defenses.

Remember that the bacteria that causes rainrot in horses can spread from horse-to-horse and horse-to-human. Make sure you wear disposable gloves when treating rainrot in your animals.

Where Does Rainrot Strike?

The telltale bumps of rainrot typically appear on your horse’s back first, but they can easily pop up anywhere and everywhere on his body. That includes his face, rump, and legs.

These crusts, lesions, and scabs can be itchy or painful. They often contain pus. You’ll notice bald patches with hair coming off in clumps. Rainrot can be frustratingly persistent and can lead to other, more debilitating infections in vulnerable horses.

So, while not every horse will get rainrot, it makes sense to do what you can to prevent it. As with any battle, it helps to understand your foe and choose your weapons wisely.

Causes and Contributing Factors

Any time the skin’s outer layer breaks down due to minor cuts, scratches, or abrasions, rainrot can occur. This skin’s susceptibility can be further aggravated by continuous exposure to heat and moisture—such as a horse might experience in daily turnout in wet, warm weather. This triggers a bacterial invasion and an inflammatory response.

In most regions, the spring and summer seasons typically provide the perfect conditions for rainrot. This is due to frequent rain, high humidity, and warmer temperatures. These conditions allow the bacteria to thrive.

If you live in a tropical zone, rainrot is more likely to be a year-round problem.

Because rainrot spreads easily—across a single horse’s body and from horse to horse via shared equipment—you can quickly go from one case to several in a short period of time.

Three factors increase susceptibility to rainrot—youth, continuous exposure to wet conditions, and a weakened immune system (most often seen in older horses and those recovering from illness).

Make sure to keep a close eye on horses with PPID. This is not only because changes in their immune systems, but because their hypertrichosis (thick hair coat and delayed shedding) can increase the risk of rain rot.

Diagnosis and Treatment

Rainrot is common enough that most horse owners and managers recognize the signs and initiate treatment accordingly. And, for the most part, this is safe to do.

However, rainrot can sometimes resemble other skin disorders, and vice versa. Rainrot that resists treatment might not be rainrot at all.

To definitively diagnose an infection of D. congolensis, your veterinarian can examine the lesions to rule out other conditions such as ringworm or a staph infection. This could involve taking sample scabs or skin smears to examine under a microscope for the presence of the offending bacteria.

In healthy horses, mild to moderate rainrot usually subsides on its own within two to three weeks if contributing environmental factors are removed. The scabs and hair will fall off, but the raw skin should heal and new hair growth should emerge within about 10 days.

If your horse has only a small patch of rainrot and the weather is drying up, waiting it out can be a reasonable treatment approach. Stubborn cases, however, might need to be addressed.

Treating Rainrot

You might hear about “home remedies” such as mouthwash, white vinegar, rubbing alcohol, hydrogen peroxide, essential oils, and even homemade antifungal medications for stubborn rainrot. Resist the urge to try these. Not only are most of them ineffective, some can irritate or damage your horse’s skin even further.

Instead, do the following to treat rainrot:

Environment—Remove the affected horse from any location that is damp or wet. This doesn’t mean your horse needs to be shut indoors, just ensure he has access to (and uses) shelter or is brought in when it starts raining. A light, breathable sheet can help protect him from rain without trapping moisture against his skin, which would make matters worse.

Skin Care—Gently dislodge the scabs. Soak the lesions until they soften and the scabs slide free from the coat, together with the administration of appropriate antibiotics (such as penicillin) by your veterinarian. Some veterinarians recommend using plain warm water for the first few soaks to loosen and remove the largest amount of crusts and scurf. Because the affected area can be very painful, be gentle. Don’t use brushes on the area.

Resist the urge to “pick” the scabs off the skin. The scabs should be soaked so they can be rinsed off the skin or come off with very gentle traction. This softening might take several soakings. You can use the showerhead setting of your garden horse nozzle to help facilitate the loosening of the scabs.

Take measures to kill the bacteria. You can clip thick hair around the lesions and use a prescription antibacterial shampoo (such as a chlorhexidine product) to help kill the bacteria. It is best to dilute the antibacterial soap in warm water and apply that mixture to the skin. Then rinse the skin thoroughly. This can help you avoid irritation caused by the shampoo. Pat the skin dry instead of rubbing the area.

If your horse ends up with widespread bald patches, it might be necessary to protect the bare skin with a thick antibacterial ointment. Check with your veterinarian for products or recommendations.

Prevent the Spread of Rainrot

Isolation of the affected individual is the most effective way to prevent the spread of rainrot. But that’s not always easy to do.

Because the causal organism can be transmitted to humans, anyone handling a horse with rainrot needs to wear disposable gloves and/or wash their hands afterward. Additional biosecurity measures include cleaning, disinfecting, and drying any tack, grooming tools, or other gear that have come into contact with the infected horse. Also avoid sharing these items used on infected horses with others.

When rainrot coincides with fly season, it’s also time to step up your insect control program. Flies or mosquitoes that land on an infected horse’s coat can easily transmit the organism responsible for rainrot to others. Therefore, it’s smart to apply insecticides frequently and use barrier clothing such as fly masks, sheets and boots.

Tips for Protecting Pasture Dwellers

Outdoor living is generally very healthy for horses. But those animals that are continually under the elements are more prone to the conditions that cause chronic rainrot. What can be done for horses living outdoors 24/7? Here are some suggestions.

Provide some shelter for your horses to get out of the rain from the hooves up.
Ensure that your horses have access to sunlight, which will dry the haircoat.
Maintain good nutrition.
Pay particular attention to the skin under blankets or sheets.
Practice good insect control. Rainrot often starts with microtrauma to the skin, and insects are the biggest offenders. Anything that causes nicks, cuts, or scratches can lead to the infection, including contact with thorny plants or stiff brushes.
Seek better accommodations for susceptible horses. Some individuals seem to be more severely affected than others and require special care.

Final Words

Rainrot can cause serious skin issues. However, you can take steps to prevent or control this issue in your horses. Remember to protect yourself and your other equids when rainrot does rear its head. Use gloves or wash your hands when handling animals with rainrot, and don’t share grooming tools, blankets, or tack among your herd.