Summer Eczema or Summer Seasonal Recurrent Dermatitis, known commonly as Sweet Itch, is believed to be caused by an allergic reaction to the saliva of Culicoides, a biting insect of which there are more than 50 different species, known as midges, gnats or "no see'ums."In Australia, it is called Queensland Itch.
Culicoides are active in the morning and early evening hours throughout the months of March through October, although in mild winter years their activity, and the consequent misery they cause to affected animals, can go on all year.
Thousands of horses throughout the world suffer from this allergy, which is caused by the bite of the female Culicoides, usually along the crest, the dock and belly. The affected areas are covered with small pustules with serum oozing from them, which dries to a crust. The intense itching they create causes the affected horse to scratch, often to the point of bleeding. As the horse continues to rub, the hair is lost and scabs form and the skin takes on a scaly appearance. Continued scratching can allow infection to set in.
Once a horse has developed an allergy to the saliva of the female Culicoides, the allergy will remain with them the rest of their lives, making treatment a long term commitment for owners.