If a person's sweat smells like ammonia, then there is nothing to worry about because sweat naturally has ammonia in it, according to WebMD, and some people have enough ammonia in the sweat for it to actually smell. During intense exercise sessions, the body will produce more ammonia than it usually does so many people with extra amounts of ammonia in their body will now have enough ammonia to produce a smell.
The New York Daily News reports that ammonia, also known as NH3, is a "nitrogen breakdown product of amino acids in the body" and is secreted through the kidneys and urea as well as through sweat. The news site also states that people tend to notice the ammonia sweat smell most often when they exercise indoors because there are not as many environmental smells or wind to take the smell away.
Surprisingly to some, the smell seems to be preventable. The New York Daily News spoke with a doctor who said that it would be possible to eliminate the smell by focusing on what a person eats before they begin intense exercise. It is important to eat carbohydrates before an intense workout for fuel. People who eat pre-workout meals including carbohydrates and drink plenty of water find that they do not have the ammonia sweat smell or have a much less pungent version.