Rain scald is a skin condition caused by Dermatophilus congolensis – an organism that is widespread. It is common in warm humid conditions, and appears usually after a few days of rain. The organism survives well on pasture, and is spread via direct contact betwenn horses, or indirectly by rolling in moist/muddy areas and by flies. Symptoms include areas of hair loss, and small irregular scabs of matted hair (which when removed leave moist inflamed skin exposed) – usually in areas that retain wet – ie along the back and flanks – or areas that contact wet abrasive grass – ie muzzle and lower legs.
In horses prone to this infection, drying legs after exercise and hosing helps. Horses on good balanced diets with no external parasites tend to be more resistant to this infection.
Soaking affected areas in 1% Potassium alum (KOH) is very effective, as is soaking in Zinc sulphate solutions. A period of fine weather usually kills this infection. A course of antibiotics may be necessary in severe infections – talk to your vet.