Q: My horse has patches of hair missing, especially on his croup. It’s going around the barn. Some people keep telling me my horse has fungus, others say rain rot. Is there a difference? How can I treat it?

A: Rain rot or Fungus? "Fungus" is a fungal infection and is seen in horses as ringworm, but it is pretty rare. Unfortunately, a lot of people use the term "fungus" to describe a wide variety of skin conditions when, in reality, it is usually a bacterial infection or a sensitivity to something in the horse’s environment.

Rain rot is a bacterial dermatitis, not a fungus, and is usually caused by the organism Dermatophilus congolensis. This bacteria, although more prevalent in warm moist times of year, can cause problems year round. It creates a scabbed over lesion, which when pulled, the scab comes off with a tuft of hair. The bacteria lives under the scab, therefore the scabs must be dislodged to treat the disease. This disease is highly contagious and grooming instruments and tack used on horses with rain rot should be cleaned and disinfected thoroughly before being used on uninfected animals.

As with most dermatologic conditions, this problem can often be prevented by daily proper grooming.

To treat rain rot in horses, use a medicated shampoo. Some work better than others. Betadine or iodine scrub is not as effective as it sounds and is too caustic to use on many horses.  In general, it is not a good choice. Consult your veterinarian if you are unsure of which shampoo to use. Apply shampoo and water to the area and lather. Let it set for 10-15 minutes in order to soften and loosen scabs, then add more soap/water and scrub with a rubber curry mitt to gently remove the scabs. Do not pick at the scabs; they can be very painful. Rinse the area. Scrape dry or use a clean towel.

Do this twice a week for 2-3 times. The condition can often look worse before it looks better because the scabs and pre-existing damaged skin come off and it may look like the lesions are spreading.  If you have any concerns, call your veterinarian for an evaluation.  Some cases require antibiotics for full resolution.