A range of variables, including diet, water consumption and kidney function as well as overall health, determines the smell of urine. Healthy human urine does not usually have a strong smell. The ammonia smell that urine sometimes produces is a possible sign of dehydration or illness.
Healthy urine is 95 percent water and 5 percent uric acid and other metabolic wastes. That 5 percent is what gives urine its distinctive smell. When an individual is dehydrated, his urine becomes more concentrated, and the amount of uric acid and waste in the stream rises. Diabetics may have urine that smells sweet, as the body excretes excess sugar as a waste product.
Other conditions, such as urinary tract infections, sexually transmitted diseases and kidney problems, can also affect the odor of urine; however, it is not uncommon for healthy people to notice a change in their urine's smell. A diet high in protein can cause urine to have a stronger smell, as the body naturally produces ammonia when it metabolizes protein. Additionally, foods such as asparagus, garlic, onion, tuna and coffee contain a sulfur compound called methyl mercaptan, which, when broken down, produces a pungent odor. Methyl mercaptan is what produces the skunk's characteristic odor.