Conditions or ailments that are the cause of a problem that you see - your observation.

Your vet may diagnose

Culicoides Hypersensitivity

Synonyms: Equine Insect Hypersensitivity (EIH), Kasen, Sweet Itch, Summer Eczema, Queen's Land Itch, Insect-Bite Hypersensitivity (IBH)


Culicoides (a/k/a buffalo gnats, humpies) are small biting flies that are mostly active at night. They are usually found close to a water source, especially running water. They are aggressive biters that feed in specific areas on the equine body. The areas commonly affected are the ears, belly, and topline, especially the mane and tail base.

Culicoide hypersensitivity refers to an allergic reaction that is seen in a fairly high percentage of horses that are bitten by these gnats. Horses that suffer from allergy to these bites become intensely itchy. They aggressively rub and scratch the affected areas. The hairs become rubbed out, the skin becomes thickened, inflamed, red, crusted and scaly. In severe cases, the affected areas may bleed from the trauma induced by scratching.

Diagnosis is fairly easy and is determined by hair loss in these typical locations, along with the presence of these biting midges.

Treatment involves recognition of the cause and management to reduce exposure. Management changes are the most important part of treatment. This includes reducing exposure to the biting flies by stabling at night, using fans to keep air movement in the barn, and the use of topical insect repellents. Sheets and masks may be helpful.

Steroids and antihistamines are recommended in more severe cases to reduce itchiness and irritation.

my vet's role


The prognosis is fair with prompt treatment and management changes. Some special management and treatment may be required long-term.

my role


I might observe

You might make these observations when a horse has this condition.

Very Common
Less Common
more observations

Questions To Ask Your Vet:
  • Will this affect my horse for life?
  • Might hyposensitization therapy be helpful?

Prevention requires management to decrease the exposure of biting midges to horses. This includes the use of fans, screens, fly repellant and fly masks and sheets as needed. Keep horses in protected stalls during times of high fly activity.

further reading & resources

Author: Doug Thal DVM Dipl. ABVP