To naturally cure rain rot, mix a 16-ounce bottle of mineral oil or baby oil, a 1/2-ounce bottle of tincture of iodine, and a 16-ounce bottle of 3 percent hydrogen peroxide together in a large unsealed container, recommends Horse and Rider. Use a sponge to apply the mixture to the affected areas, and allow to sit overnight. The following day, shampoo the horse using a mild shampoo, and allow the area to air-dry in the sun if possible.
Rain rot is caused by bacteria that typically reside on a horse's coat, notes Horse and Rider. When a horse's skin is drenched with water and becomes immune-compromised, the bacteria take advantage of this situation. Horse owners must take care not to further irritate the horse's skin, as doing so can cause more infections.
Though rain rot is commonly mistaken as a fungal infection, it is caused by the bacteria Dermatophilus congolensis, reports TheHorse.com. The bacteria is dormant on the horse's skin until the skin is affected by biting insect attacks, long-lasting wetness, or high temperatures or humidity. Veterinarians can effectively diagnose rain rot by visually examining a horse's skin lesions. However, the veterinarian can make a definitive diagnosis by examining a skin scraping for Gram-positive bacteria.
Although most acute cases of rain rot heal independently, minor cases should be treated to prevent the lesions from spreading and worsening. The lesions can also make it difficult for a rider to use the horse and may cause the horse pain.