Rain Rot in Horses
By: Dr. Lydia Gray | Updated March 21, 2025 by SmartPak Equine
What is Rain Rot in Horses?
Rain rot is a skin infection caused by the bacteria Dermatophilus congolensis. Although the bacteria is present in the environment all the time, it requires a moist environment and a break in the skin to develop into the characteristic hard, painful crusts over a horse’s back and rump.
These crusts are distinctive not only because of where they occur on the horse’s body, but also because when removed, hairs stick through the scab and look like a mini "paintbrush." Rain rot is an unsightly condition that may also prevent a horse from being worked until the skin heals.
Treatment for Rain Rot in Horses
The best treatment for rain rot is removal of the scabs so that dry air and sunlight can reach the skin. Since the crusts are hard and painful, it may be necessary to soak and soften them first with an antibacterial bath. Horses that are severely affected or ill may also need injections of the antibiotic penicillin.
Preventing Rain Rot and Other Skin Conditions
Although some horses are susceptible to Dermatophilus no matter how well they are cared for, certain steps can be taken to try and avoid the infection.
- Groom horses daily, especially those wearing blankets.
- Keep all tack, brushes, and blankets as clean as possible and try to not share equipment between horses.
- Provide shelter from the rain, especially in the winter.
- Make sure all horses are up-to-date on vaccinations, deworming and other health care, and that they are at an appropriate weight.
Video on Rain Rot in Horses
In this Ask the Vet video, Dr. Gray explains what rain rot in horses is and how to prevent it from spreading throughout the stable.
SARAH: She recently started riding a horse for her trainer and the horse has rain rot. His skin is a total mess, and there is no arguing with that. But she feels like people often call any skin issue rain rot. What really is rain rot, and how would she fix it?
DR. LYDIA GRAY: I think she's said some very honest things. I do think that a lot of people see anything in the horse, and oh, rain rot. Rain rot is the term we call dermatophilosis. It's caused by a bacteria, dermatolophilus congolensis. And it's an opportunistic bacteria, in that this bacteria lives on horses, lives on you, lives on me. It's everywhere. But what it's doing is it's waiting for a break in the skin to then--
SARAH: It's waiting.
DR. LYDIA GRAY: And it's waiting for moisture. It really likes moisture. So in the winter, when horses grow a long coat, they can trap moisture under the coat and it sets up the perfect environment for the bacteria under that skin to have a little heat, a little moisture, maybe some not great nutrition, maybe some immune suppression. Cushing's horses are notorious for getting this.
And then it breaks loose. And what it looks like is classic presentation, is these paint brush lesions. So there are these crusts that are sort of rounded. And they come off pretty easy. They're a little bit painful. But if you pull the crust off and look at it, it looks like a paint brush, in that there's hairs underneath the crust.
And a horse's back might have a lot of these. And so your veterinarian is your best person to tell you for sure it's rain rot and not some other skin condition. But to help you figure out the underlying problem, because you can treat it all you want, the current problem, but if you don't fix the underlying issue, it's just going to come back.
So you've got to say maybe a blanket, a sheet to keep the wet off, maybe increasing the nutrition in the horse, maybe diagnosing and treating the Cushing's. Whatever the horse needs. And then your veterinarian will also help you with the treatment of the current condition, which is usually a combination of removing the crusts and maybe some shampoo, maybe some topical.
Rarely antibiotics, because it's not a whole horse thing. It truly is just one area. So you have to work with your vet to figure out why your horse had it to begin with, why does this horse have it, and then to get rid of it. And so it's not contagious, but when you pull up those crusts, you don't just leave them on the ground, because they have high numbers of the bacteria.
So you want to be careful with those. And it's probably a good idea not to share equipment of a horse that has that with other horses, so like a saddle pad would be a great thing. It's called a fomite. It's something where this inanimate object has the bacteria on it, and it's transitioned from one thing to another. That's a fomite. That's our word for the day.
SARAH: It feels like in all those movies that you see about viruses and stuff, where it's glowing, and you can imagine the saddle pad as just thriving with--
DR. LYDIA GRAY: They're just waiting for the next victim.
SARAH: And is it fair to say that it's only the equipment that's in the affected area? If he has rain rot on his back and he's using boots, can somebody else use those boots and have no problem, because it's not a whole horse thing, or would you say all the equipment, just keep it for him?
DR. LYDIA GRAY: For that, I would keep it just for him, because you wish things would glow. You wish, when things had viruses and bacteria and other germs, they would glow. Because think of a brush. You might brush the horse everywhere, brush the legs, and then you put the boots on. So unless you're really good about I've got a sick area brush and a well area brush, I would probably keep everything for that horse. I mean the halters, everything.