ObjectiveTo assess the efficacy of an herbal spray combining various essential oils, with a claim of mast cell stabilisation, antipruritic, anti‐inflammatory, and insect repellent effects on the clinical presentation of insect bite hypersensitivity (IBH) in horses.DesignDouble‐blinded, placebo‐controlled, randomised, cross‐over clinical trial.MethodsTwenty adult horses with clinical IBH were treated with a daily application of herbal spray or placebo for 28 days in a randomised, cross‐over fashion, separated by a>28‐day washout period. Horses were examined and scored prior to and after the completion of each treatment. Histopathology was performed on four horses. Owners kept daily diaries of observations.ResultsThe herbal spray significantly reduced the severity of all assessed parameters (pruritus, excoriations, lichenification and alopecia; P < 0.05) compared with baseline values (pretreatment) and with placebo. Owners reported improvement of pruritus in 19/20 horses (95%) with complete resolution in 17 horses (85%) following treatment. Skin biopsies showed resolution of orthokeratosis in 4/4 horses, reduced thickness of the stratum spinosum in 2/4 horses and complete resolution of histopathological abnormalities in 1/4 horses after treatment, compared with either no change or deterioration of histopathologic lesions after placebo. No side effects were observed.ConclusionsThe tested herbal spray may be an effective treatment for the management of equine IBH.

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Insect Bite Hypersensitivity (IBH, Queensland itch, sweet itch, equine summer eczema) is the most common pruritic disease of horses. It is most often caused by sensitivity to the saliva of Culicoides spp. of biting midges; however, it can also be caused by hypersensitivity to other insect species. The prevalence of IBH in horses is reported to be as high as 60% in some parts of the world. Due to the severe pruritus and effects of secondary self-trauma, IBH has animal welfare concerns, and there is currently no cure. Management of this condition is life-long, time consuming and costly. New grading systems to document disease severity are being validated, which will allow the comparison of clinical trial results of new and existing therapies. Management involves the minimisation of insect bites by use of stabling, fans, rugs and repellents. Symptomatic therapy involves the administration of systemic or topical corticosteroids, systemic antihistamines, and creams and sprays to promote skin healing and decrease inflammation. New immune-mediated therapeutics including vaccines, in addition to desensitisation procedures, show promise at controlling hypersensitivity reactions. This article will review aetiologic agents, pathophysiology, scoring systems and current and new therapies.