Horse Sweet Itch (Insect Bite Hypersensitivity)

Sweet itch is a severely pruritic allergic skin condition in horses caused by hypersensitivity to biting midge saliva. It causes intense suffering and significantly affects quality of life for affected horses.

Key Facts

Sweet itch (summer seasonal recurrent dermatitis, or insect bite hypersensitivity, IBH) is caused by an IgE-mediated allergic response to salivary proteins in Culicoides midge bites
It affects between 5–10% of horses in the UK and higher proportions in some European countries; certain breeds (Icelandic horses, Fell ponies, Shire horses) have elevated prevalence
Icelandic horses exported from Iceland — where Culicoides midges are absent — develop IBH within 2–3 years of exposure on the mainland, demonstrating that the allergy requires sensitisation through repeated midge exposure
Clinical signs include intense pruritus (itching) over the mane, tail head, ears, withers, and belly; affected horses rub and bite these areas causing hair loss, skin thickening, excoriation, and secondary infection
The condition is seasonal in temperate climates (typically April–October when midges are active) but can be year-round in warmer regions
Management relies on midge avoidance: turning out only at mid-day when midge activity is low, stabling at dawn and dusk, full-body fly rugs with belly and neck cover, and appropriate insect repellents
Symptomatic treatments include antihistamines, corticosteroids (short-term), and increasingly allergen-specific immunotherapy (desensitisation), which shows promise in reducing hypersensitivity
There is no cure; management is lifelong and must be tailored to the individual horse's pattern and severity of reaction

Welfare Considerations

Sweet itch causes intense, chronic suffering that significantly impairs quality of life for affected horses. The pruritus is so severe that horses will rub themselves raw, causing extensive skin damage, secondary infection, and permanent hair loss. The behaviour changes associated with severe sweet itch — rubbing obsessively, biting at the belly, crashing through fencing to escape, inability to stand still — reflect genuine distress rather than mere discomfort. Horses with poorly managed sweet itch suffer seasonally for years or decades. The psychological impact of constant itch is real: horses that cannot escape the sensation become irritable, anxious, and difficult to manage. Comprehensive midge avoidance — a significant management commitment — combined with appropriate pharmacological and immunological treatment can substantially improve welfare for affected animals.

What You Can Do

Implement rigorous midge avoidance: stable at dawn and dusk, use a properly fitting fly rug with belly and neck cover
Apply insect repellents licensed for equine use consistently during midge season
Discuss corticosteroid treatment with your vet for severe active cases, and ask about allergen-specific immunotherapy for longer-term management
Avoid moving Icelandic horses and other naive breeds to midge-endemic areas — sensitisation is irreversible
Support research into equine IBH immunotherapy through participation in clinical studies and welfare research funding