Ketosis can be recognized by the smell of acetone (or ethanone according to IUPAC standards for naming organic compounds) on a person's breath. How does acetone come to be in the body?
In this disease, the body produces more acetoacetate than can be metabolized. This occurs when the body uses fat instead of glucose (sugar) for energy. This can be indicative of the inability of the body to use insulin effectively to burn glucose for energy. The excess acetoacetate breaks down to acetone (a ketone) and carbon dioxide. Acetone normally passes into the urine, however, only a certian amount can be excreted in this way. Since acetone is highly volatile (think of smelling nail polish remover in a large room) it can be excreted in the breath in person's with a high concentration/excess of acetone in the body.