In a 2018 biography, author Matthew Polly consulted with medical experts and theorized that Lee died from cerebral edema caused by over-exertion and heat stroke; and heat stroke was not considered at the time because it was then a poorly-understood condition. Furthermore, Lee had his underarm sweat glands removed in late 1972, in the apparent belief that underarm sweat was unphotogenic on film. Polly further theorized that this caused Lee's body to overheat while practicing in hot temperatures on May 10 and July 20, 1973, resulting in heat stroke that in turn exacerbated the cerebral edema that led to his death.