Horse chestnut extract comes from the seeds of the horse chestnut tree and is standardized to contain a set amount of escin, its main active compound.
Escin's best proven effect is helping tighten up tiny blood vessels called capillaries and improving how well veins function. It does this partly by blocking the enzymes that would otherwise break down the structural fibers holding capillary walls together, which helps keep fluid from leaking into surrounding tissue and supports its calming, anti inflammatory effect.
Most of the strong clinical evidence behind escin, including a large research review, comes from studies on oral horse chestnut seed extract taken for a circulation condition called chronic venous insufficiency, not from topical skincare use specifically. That means the claims made for topical eye creams and leg products are a reasonable extension of that evidence, but not something that has been directly proven the same way.
Horse Chestnut Extract References
Escin, a review of its anti edematous, anti inflammatory, and venotonic properties, Drug Design, Development and Therapy, 2019
Horse chestnut seed extract for chronic venous insufficiency, Cochrane Database of Systematic Reviews, 2012
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