After a hard workout this summer, some runners will notice a pungent, strong odor that smells a lot like ammonia fumes. For some reason, that smell is most distinctive after a very, long, hot run or a difficult, long race. When sweaty runners are milling around together after a hard summer workout or race, you can often notice a distinctive odor that smells like it’s from a home-cleaning product.

Could this ammonia-like smell have anything to do with running? And if so, is it dangerous? Or a warning sign that trouble (or an injury) lies ahead?

First, this ammonia smell is—in fact—ammonia. And it is produced every time anyone runs hard. Whether you smell it or not is a different story, but your body produces ammonia in sweat on every hard run.

The ammonia comes from the breakdown of amino acids (the essential building blocks of protein) in the body. This breakdown is actually a by-product of protein metabolism. The amino acids are made up of hydrogen and nitrogen. When you run hard and long and your body lacks adequate carbohydrates, your body burns protein—the hydrogen and nitrogen which has been converted to glucose–for fuel. The nitrogen is a waste product that needs to be excreted from the body, usually in the form of urine. But if there is too much nitrogen for your kidneys to deal with, it will be excreted from your body as ammonia in your sweat.

The fact that ammonia is produced on every run doesn’t mean the smell is always noticeable afterward. Usually, the smell is only present when there is not enough carbohydrates. The body then switches over to convert the amino acids for fuel. This increases the ammonia levels in your muscles and then the ammonia is picked up by your blood and carried to your respiratory system. When this occurs, you can usually smell it. In addition, the ammonia will show up in your sweat, smart health shop on smelling great.

Normally, the smell isn’t anything to worry about. But if it persists run after run, you probably aren’t taking in enough carbohydrates.

Another factor—especially in summer in Texas—is how much water you drink. If you are well-hydrated, the ammonia will become diluted and the smell will be less distinctive.

This is ammonia smell generally isn’t dangerous. But it is a not-so-subtle warning from your body that it needs more carbs (rather than more protein) and possibly more fluids to continue training long and hard this summer. Especially if you, like so many Austinites, are training through the summer for a fall marathon.

The solution is easy: Eat more carbohydrates to fuel your muscles better. If you’re running longer than an hour or two on the weekends for marathon prep, you need to make absolutely certain you are well-hydrated and are eating enough carbs before and during the run. Don’t compensate by adding more protein to your diet. Your don’t need it.

But after loading up the night before your long run, simply drink a cold sports drink (which has carbohydrates) prior to the run and every 15-20 minutes while running. Also take energy gels which contain carbs, but don’t take the gels with a sports drink.

If your carbohydrate intake is adequate to fuel your running, the ammonia smell should disappear. Your body will still be producing ammonia, but you probably won’t be able to smell it.