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Sweet Itch in Horses: The Science Behind the Itch (and What Actually Helps)

by Valerie De Clerck on Jul 06 2026

Sweet itch is driven by IL-31 from skin cells responding to the allergic cytokine environment, not by direct midge allergen contact. This is why antihistamines have poor efficacy in horses (Marti et al., 2023). IBH-affected horses have nearly 2x the circulating eosinophils of healthy controls, confirming this is a whole-body allergic response, not just a local skin condition (Frontiers in Immunology, 2024). Physical midge avoidance (close-weave rug, dawn/dusk stabling, fans) is the single most evidence-based management tool. A 2024 placebo-controlled trial found allergen immunotherapy produced >50% improvement in 89% of treated horses by year two. The most promising long-term treatment on the horizon, though not yet commercially available.