Are you saying the smell is coming from the breath? Have you asked your client what his or her diet is composed of? It may be what Joseph was hinting. If your clients diet is composed of mostly protein and fat with very little carbohydrates, your body is put into a ketogenic state, where ketones (derived from the breakdown of fat) are used as an individual’s main source of energy. It leads to a change in the person’s breath that is maintained until the diet is changed to include more carbohydrates.