Ash, specifically referring to the bark, leaves, or other parts of the Fraxinus species (commonly known as ash trees), has been used in traditional medicine systems for various ailments, including chills. In some European herbal traditions, ash bark tea or infusions were administered to help "break a fever" or relieve chills, often as part of broader remedies for colds, intermittent fevers, or rheumatism. The rationale was largely based on ash's supposed diuretic and anti-inflammatory properties, as well as its use as a “cooling” herb to help balance bodily humors.

However, there is minimal scientific validation for these uses. Few, if any, modern clinical studies have examined the efficacy of ash for treating chills or fevers specifically. Most of the evidence remains anecdotal or based in ethnobotanical records. Some laboratory studies have identified potential anti-inflammatory compounds in ash bark, but these findings have not translated into robust, clinically relevant evidence for treating chills or fever in humans.

In summary, the use of ash to support or treat chills is primarily justified by traditional herbal practices, with little to no high-quality scientific evidence backing its efficacy for this particular condition.