An article about what causes hot flashes in women during menopause cites a study by Dr. Robert Freedman and colleagues at Wayne State University. They theorize that women who are affected have a very narrow "thermoneutral zone" - the temperature at which the body is neither sweating nor shivering. Estrogen appears to widen the zone. According to the article, no one knows exactly what happens to the body during a hot flash, but it appears that changes in brain chemistry have something to do with it.