A person with severe untreated diabetes may have breath that smells like nail polish remover. Why does this occur?

Diabetes mellitus is due to a lack of insulin (type I) or due to decreased insulin function (type II). The end result is that glucose is not available for metabolic pathways. As a result the liver rapidly breaks down fat into ketones to use as a fuel source. The 3 most important ketones are acetone, beta-hydroxybutyrate, and acetoacetate. The overproduction of ketones causes them to accumulate in the blood and urine and turn the blood acidic (the ketones are acids). The acetone produced in the liver is the same acetone used as nail polish remover.