The Scientist: Susan Biehle-Hulette, Ph.D., a biochemist at Procter & Gamble
The Answer: There are several reasons that your sweat might smell like ammonia. Most of them are nothing to worry about, but it could be a sign of something more serious.
When you exercise, your body uses carbohydrates for fuel. That’s why you often hear about people carbo-loading before a marathon. But during long, strenuous workouts, such as marathons, or even a full-tilt day at the gym, sometimes the body needs to dip into its protein stores for added energy. When the amino acids in proteins are broken down, one of the by-products is ammonia, which is then excreted in your sweat. Hence the stench.
If you are on a low-carb, high-protein diet, you increase the chances that your body will turn to amino acids because there aren’t enough carbohydrates in your system to sustain the activity. Eating starches before a workout will give your body adequate reserves to meet your energy needs without breaking down protein. In addition, dehydration can exacerbate the problem by increasing the concentration of ammonia in your perspiration. Drinking more water while you exercise will dilute the ammonia and minimize the odor.
If neither what you eat nor what you drink has any effect, you should probably get checked out by your doctor. The smell could signal an electrolyte imbalance, or damage to your liver or kidneys.