Everything you need to know about sweet itch in horses

Sweet itch, also known as Culicoides hypersensitivity, is a common seasonal skin allergy in horses and ponies. It results from an immune reaction to the saliva of biting midges (Culicoides), causing intense itching, hair loss and skin damage around the mane, withers, tail, face and ears. Over time, the skin thickens, folds develop, and the hair becomes sparse and coarse, often with scaly dandruff.

The condition typically flares up from late March through to October or November, depending on how warm it is. While not life-threatening, sweet itch can severely affect a horse’s comfort and wellbeing. Those suffering may show behavioural changes such as irritability, aggression or restlessness due to discomfort. Some may also lose weight.

What causes sweet itch in horses?

Sweet itch occurs when proteins in midge saliva trigger the horse’s immune system, causing an allergic reaction. It’s the saliva, not the bite itself, that causes inflammation, leading to an overwhelming urge to rub, scratch and bite the affected areas. Repeated rubbing can lead to crusty, sore or infected skin.

Culicoides hypersensitivity is the most common equine skin allergy in the UK and affects an estimated 5% of the UK horse population. Certain breeds, especially native ponies such as Shetlands and Welsh, are more susceptible. Genetics play a role: if a parent has sweet itch, a foal is more likely to develop it.

Environmental factors also play a part, including humid weather, waterlogged fields where midges breed, proximity to standing water, sheltered or wooded grazing, and the times of day when midges are most active – dawn and dusk.

Diagnosis of sweet itch

Symptoms of sweet itch in horses vary widely. Some horses will be badly affected by a couple of bites, while others may experience no reaction at all.

Although the outward signs of sweet itch are recognisable, other allergies can show similar symptoms – such as dermatitis from rugs or bedding, food-related allergies and reactions to other biting insects.

A vet may recommend further testing to confirm the cause. Intradermal allergy testing involves injecting small amounts of midge extract into the skin to observe any reaction. This can help identify other allergens involved and narrow down potential triggers.

How to treat sweet itch in horses

There is currently no proven sweet itch cure, so long-term management remains the most reliable approach for sweet itch treatment. Preventing midge bites is far more effective than treating the reaction afterwards.

These sweet itch management strategies are key to keeping a horse comfortable.

• Sweet itch rugs: Lightweight, ultra-fine mesh sweet itch rugs have elasticated edges that cover the body and neck, preventing midges from accessing the skin. A well-fitted rug should be worn whenever the horse is outside. Keep at least one spare rug for washing and rotation.
• Turnout management: While not feasible for every yard, stable horses from late afternoon until early morning during peak midge activity if possible. Midges struggle to fly in winds over 4mph, so open, breezy pastures are ideal. Avoid woodland and standing water, where midges breed.
• Fly sprays and masks: Turn out in a fly mask and apply insect repellent spray. Pyrethroid- or permethrin-based repellents are often the most effective. DEET can work but may irritate horses who have scratched their way to broken skin – always patch-test first.
• Topical treatments: Soothing shampoos and emollients reduce itching but do not prevent bites. Steroid creams may help relieve itching and irritation but should only be used under veterinary advice. Benzyl benzoate is a stronger topical option and can work well on early-stage lesions if the skin is still intact – particularly in less-sensitive horses or those with fewer bites.
• Antihistamines and immunotherapy: These can be prescribed by a vet to reduce swelling, itching or the severity of allergic reactions.
• Human midge repellents: These are often safe if patch tested first. Anecdotally, Avon Skin So Soft is an effective sweet itch remedy and has been used by the British Army for fly protection.

As severe cases of sweet itch can lead to secondary skin infections, self-inflicted injuries from rubbing or behavioural issues requiring veterinary intervention, ensure your horse insurance is up to date to help manage the cost of any treatment.

What to feed a horse with sweet itch

Balanced nutrition complements other sweet itch treatments for horses, supporting recovery and overall wellbeing during the season.

Diet alone isn’t a sweet itch cure, but it can support skin health and help reduce inflammation. Omega-3 and omega-6 fatty acids from flaxseed or fish oil, along with vitamins A, E and zinc, support a healthy coat and skin. Ensuring adequate, good-quality protein is also important for skin repair and hair regrowth.

A forage-based diet that supports gut health may help reduce inflammatory responses, while reducing sugar-rich feeds can also be beneficial.

Some owners use home remedies such as cider vinegar or garlic in the feed to deter midges. These are generally safe and may offer minor benefits, though there is little evidence that they prevent bites. However, garlic can still support overall horse health due to its antioxidant properties.