Sweet itch, also known as Summer Seasonal Recurrent Dermatitis or Equine Insect Bite Hypersensitivity, is the most common allergic skin condition in horses. Sweet itch can affect all breeds and types of horses, ponies and donkeys and can be genetic meaning some horses are at an increased risk of developing the condition. Some breeds for example Belgian warmblood1 and Icelandic horses2 as well as native ponies such as the Exmoor3 have been found to be at an increased risk.
Sweet itch is caused by an allergic reaction to the protein in the saliva of biting insects. This causes the immune system to attack its own cells and leads to the extreme reaction.
In the UK insects that cause sweet itch are the midge (Culicoides) and potentially the black fly (Simulium). Horses are most commonly affected between March – November when the biting insects are most active.