Los Angeles County West Vector & Vector-Borne Disease Control District

Biting Midges
(Sweet Itch)

Sweet Itch

What is Sweet Itch?

    Sweet Itch, or Summer Seasonal Recurrent Dermatitis (SSRD), is a problem that affects thousands of horses, ponies and donkeys worldwide. Within recent years, this condition appears to have migrated into the Palos Verdes Peninsula as well as other regions of Southern California. Virtually all breeds and types of ponies and horses can be affected by Sweet Itch, from Shetland ponies to heavyweight draught horses.

    Sweet Itch is an allergic condition that results when an animal develops a hypersensitive reaction to a protein in the saliva of a biting midge. Sweet Itch can become quite severe and unsightly, thereby reducing the suitability of the animal for riding or show.


What are the signs of Sweet Itch?

Signs include:

  •  Severe pruritis (itching) 

  •  Hair loss

  •  Skin thickening

  •  Flaky dandruff

  •  Exudative dermatitis (weeping sores)

  •  Secondary infection at site of sores

The midline of the belly, top of the tail and mane are the areas that are most commonly affected. The itching can become so severe that there can be a marked change in temperament ranging from restlessness to lethargy and increased agitation. Horses usually show signs of Sweet Itch between the ages of one and five. It is probable that hereditary predisposition is a factor in the development of Sweet Itch.


Biting Midges



       Biting midges, also known as ‘punkies’ or ‘no-see-ums’ are small, biting flies with an average wing length of less than 2 mm. In the United States several species (of the 1,000 or so that exist) of the biting midge (genus Culicoides) are responsible for Sweet Itch.    

      While both male and female adult biting midges feed on nectar, the females require blood for egg production. The females possess piercing, sucking mouthparts that are capable of obtaining blood meals from a variety of hosts. Biting midges are most active at dawn and dusk but may feed at any time during humid, cloudy days.


Where are biting midges found?

     Midges usually do not fly far from their breeding grounds. Biting midges dislike hot, dry conditions, strong wind, heavy rain or bright sunshine.  Breeding sites include moist, decaying vegetation or wet soil (e.g. mud polluted by animal excrement). Culicoides larvae are capable of surviving severe frosts but do not survive prolonged drought conditions.



Diagnosis of Sweet Itch

   The symptoms and its seasonal nature are strong indicators of Sweet Itch.  However, symptoms can persist well into the winter months, with severe cases barely having cleared up before the condition starts again in late winter and early spring.  If you suspect that your horse may have Sweet Itch, please consult a veterinarian.

Is There a Cure for Sweet Itch?

    Unfortunately, there is no cure for Sweet Itch. Once an animal develops the allergy, it generally faces a ‘life sentence’. The animal’s comfort and well being are down to its owner’s management.



Minimize Midge Attack

  • Avoid marshy, boggy fields. If possible, move horse to a more exposed, windy site (e.g. bare hillside or a coastal site with strong onshore breezes).

  • Ensure pasture is well drained and free from rotting vegetation (e.g. muck heaps, old hay feeding areas, rotting leaves)

  • Stable at dusk and dawn when midge feeding is at its peak. Close stable doors and windows to prevent midges from entering.

  • Install a large ceiling-mounted fan in the stable to create less favorable conditions for the midge

Use an Insect Repellent

  • Horse owners should use repellents approved for use on horses, but the effectiveness of some formulations under certain conditions (e.g., rain, perspiration) may be limited. Insect repellents can be effective for humans and have some limited value for horses as well.

  • Products containing these active ingredients typically provide longer-lasting protection than others:

    • Picaridin (KBR 3023) - up to 20%

    • DEET (N,N-diethyl-m-toluamide)) - up to 20%

Use an Insecticide

  •  Apply a veterinarian-prescribed insecticide such as benzyl benzoate or products containing permethrin. 

Use a Veterinary Blanket

  •  Use of a veterinary blanket can be effective against Sweet Itch and is an alternative to using insecticides, oils or greases.



Minimize Allergic Reaction

  •  Use of veterinarian-prescribed corticosteroids to help reduce inflammation caused by the immune response.

  •  Use of veterinarian-prescribed antihistamines may help to reduce allergic reaction.

  •  Soothing lotions such as Calamine Cream, ‘Sudocrem’ or steroid creams may aid in reducing inflammation.


For Further Information:

For additional information on Sweet Itch and suggestions from other horse owners, contact your local veterinarian.