Rain rot is a term used to describe an infection of the skin caused by fungi that grows when wet. It is most common in areas with high humidity, warm temperatures, and heavy rainfall. In susceptible horses, rain rot can develop during any season, but it is more prevalent in spring and summer. Prevention involves good grooming; brush and comb the horse regularly to remove accumulated mud, dung, and urine, and avoid letting them sweat excessively. If rain rot does occur, treatment includes antibiotics and plenty of rest.