What is Sweet Itch?


Summer Seasonal Recurrent Dermatitis (SSRD) or “Sweet Itch” in horses is an allergic response to biting flies/midges of the genus Culicoides.  Most horses are bitten by these insects but only some will have an allergic response.  Sweet itch is seasonal in colder climates, may be nonseasonal in warmer climates, and may affect horses of any age, sex, or breed.  Although it has not been verified, some believe that this condition may have a genetic component.

Clinical Signs and Symptoms of Sweet Itch


Lesions will vary depending on where the specific type of insect feeds.  Most often, however, lesions are noted on face/ears, mane and tail areas, abdomen (ventral midline), and chest.  The horse may be extremely pruritic (itchy) and will have areas of alopecia (hair loss), excoriations, and some severe lesions may even drain serum.  Many times a horses’ behavior is noted to change – they can become lethargic or very agitated (especially when insects are present).  Horses will scratch on fences or trees to the point that they rub out their mane and the hair at the top of their tail.  Some people notice that their horses will drag themselves along the ground to scratch their chest/belly or will sit like a dog and spin to scratch the top of their tail.  Eventually the skin becomes thickened and folded and the hair over affected areas is sparse and coarse.  Sometimes the lesions will completely heal over the winter but return with the return of the insects in the spring or summer.

How can I treat or prevent Sweet Itch?


Preventing or minimizing sweet itch in your horse is no small task.  The most important step is to decrease the exposure your horse has with the biting midges.  This can be done by killing the insects or by other horse/barn management steps.  The following are some management steps that you can take to make your horse more comfortable:

  • Have multiple fans in a horse’s stall (ceiling and wall mounted) as the breeze makes it harder for the flies to land on the horses.
  • Insect proof your stalls and stables with fine mesh screens.
  • Stable your horse at night or at least in the hours around dusk and dawn.
  • Use protective “fly wear” for your horse – this includes fly masks (with ears), leg wraps and fly sheets (make sure the sheets cover as much of the abdomen as possible).
  • Since Culicoides midges breed in wet areas, maximize drainage of pastures and be sure to keep water troughs clean.


The best insecticides are those containing pyrethrins or pyrethroids (DuraGard by Absorbine or Knock-out Spray by Virbac).  Anecdotal reports suggest that consistent use of Fipronil (Frontline spray, Merial) can be used for Culicoides sensitivity.  Avon Skin-so-soft mixed with equal parts water has also been used as insect repellent.  Use caution with Skin-so-soft as dermatitis has been reported in some horses.

Itch/Allergy Treatment

The first step in treating skin irritation is topical products that soothe itching and moisturize skin and coat.  One such product that has received rave reviews is Wahna Win, a skin and coat moisturizer that is applied directly to the horse’s coat.  There are anecdotal reports that DMSO can alleviate pain and itching as well.  Feed through fatty acid supplements have also been suggested.

Although there are multiple options to control pruritis, corticosteroids remain the most useful product to alleviate itching.  As steroids do have side effects, they should only be used under the supervision of a veterinarian.