Hi, Brenda. An ammonia smell in sweat and urine is produced by protein metabolism. The smell is produced when amino acids (the building blocks of protein) are metabolised for energy. All amino acids contain nitrogen (N) and when they are metabolized the nitrogen molecules are removed and they combine to produce ammonia (NH3). The ammonia will then be excreted in the urine or sweat. There are several possible reasons why this happens sometimes, but not all the time. If your water intake is too low the ammonia will be more concentrated and may become detectable by smell. If your protein intake is very high or you take protein supplements, the ammonia smell may be more detectable. Another possibility would be that you have no, or very low carbohydrate intake on the days when you smell the ammonia. A banting-type diet could easily cause this because the body is utilizing protein for energy instead of carbohydrates, which will produce more ammonia. If you would like to avoid the ammonia smell, increase your water intake and make sure you consume some healthy carbs when you train.