Aescin (also spelled escin) is a mixture of saponins derived from horse chestnut (Aesculus hippocastanum) seeds, widely used for its vascular-protective properties. The use of aescin to support or treat capillary weakness is primarily supported by scientific evidence, particularly in the context of chronic venous insufficiency (CVI) and related vascular conditions. Multiple randomized controlled trials and meta-analyses have shown that aescin can reduce capillary permeability, edema, and symptoms such as leg swelling and heaviness. The mechanism is believed to involve strengthening capillary walls, improving venous tone, and exerting anti-inflammatory effects. For example, a meta-analysis published in "Cochrane Database of Systematic Reviews" (2012) concluded that horse chestnut seed extract (standardized to aescin content) is effective in reducing leg pain and edema in CVI, conditions often associated with capillary fragility.

The European Medicines Agency (EMA) has recognized horse chestnut seed extract as a traditional herbal medicinal product for the relief of symptoms of discomfort and heaviness of legs related to minor venous circulatory disturbances. While not all studies are of the highest quality, the overall evidence base is considered moderate to strong for its effects on vascular permeability and capillary stability. Adverse effects are generally mild and rare when standard preparations are used. Therefore, aescin's use for capillary weakness is scientifically validated, with a reasonable level of evidence supporting its efficacy.