A horse I am riding has a skin condition and I have no idea what it is. It is in the base of her tail and on either side of the tail on the back of her. They are large, black flakes that look like skin and dirt? She is also sensitive to touch those areas. Could it be rain rot? On either side of the tail it is almost greasy looking with black specks. Does anyone know what it is? she came from a rescue a few months ago and had it there, too.