There are many causes of tail rubbing, ranging from gnat irritation and skin disease to sunburn and internal parasites.
A horse's tail punctuates his beauty and elegance with its carriage, thickness, and gloss. Owners go to great lengths to keep their horses' tails pristine. So when a horse rubs his tail into a frayed or hairless mess, there is motivation to get to the bottom of the problem as quickly as possible. When faced with a horse that persistently rubs his tail, one question to consider is the time of year this occurs. Is it seasonal or is it an incessant behavior that appears year-round?
Seasonal tail rubbing is often a result of a hypersensitivity response to certain insects. Christine Rees, DVM, Dipl. ACVD, a practitioner at Equine Allergy and Dermatology of Texas, has many occasions to evaluate horses with pruritus (itching). She notes, "Reactions to insects are caused by hypersensitivity to salivary antigens (proteins) in the insect bite. These proteins elicit release of inflammatory mediators that cause irritation and tail rubbing. The most common insects to cause tail rubbing are the Culicoides gnats."
Culicoides hypersensitivity in horses is also referred to as "sweet itch." In severe or advanced cases, itching is not just confined to the tail; the horse also rubs mane, neck, and chest in response to the systemic reaction generated by gnat bites. At times tail rubbing goes beyond just broken tail hairs; the tail might become completely denuded of hair, with self-inflicted trauma sufficient to create bleeding areas and a "rattail" appearance. Persistent, chronic