You might be surprised to learn that human sweat in its purest form is basically odourless. Sweat has got a bad rep for being stinky stuff, but it’s actually the rapid proliferation of bacteria breaking sweat down into acid that causes the unpleasantness to follow soon after sweat builds up, rather than anything in the makeup of the sweat itself.
There are times when sweat can smell a bit ‘off’; if you’ve recently been eating pungent foods like garlic or curry, for example. But sometimes athletes report their sweat having a very striking and unpleasant chemical-like ammonia scent during or after workouts.
This is likely to have a specific cause…
Sweating when your carb intake is low (or your protein intake is high) could cause ammonia-smelling sweat
Ammonia is a natural by-product of protein breakdown and, in the usual run of things, it’s converted to urea in the liver and then you pee it out. Simple.
But, if your body has to start to burn a lot of protein for some reason, ammonia can build up to levels which cause your body to offload some of it through your sweat as well as your urine.
Usually this is due to inadequate carbohydrate intake, or excessive protein consumption in your diet. It’s thought that inadequate fluid intake can worsen the issue because your sweat becomes more concentrated, so the ammonia smell is increased. You also pee less, meaning you’re passing out less ammonia through that route and so begins a vicious cycle.
Who’s likely to suffer with smelly sweat?
It seems that athletes who are purposefully eating a low-carb or ketogenic diet, or those unwittingly not meeting their carbohydrate needs, are more likely to experience this issue as their glycogen (carbohydrate) stores are more prone to being depleted, leading to a greater breakdown of protein to fuel activity.
Ultra-endurance athletes could also find themselves with stinky sweat during very long efforts if they burn through most of their endogenous (internal) fuel stores and fail to eat enough to keep up with their energy demands.
In terms of peer-reviewed research on the topic, there doesn’t appear to be a whole lot out there. Most of what I read in writing this article is anecdotal, although my searches did turn up this paper studying the effects of a low-carb diet on sweat ammonia concentration during exercise.
I also came across this interesting article suggesting that women appeared to find the smell of sweat from men on a diet containing less red meat more attractive than the sweat from those eating lots of red meat! Whether this has anything to do with protein breakdown and ammonia smells is not immediately clear, but it’s probably worth bearing in mind if you’re a single man…
How can you stop your sweat smelling of ammonia?
Whilst it’s unlikely to be a sign of anything horribly wrong, sweat that smells of ammonia is not ‘normal’ and is something to investigate.
It’s worth being aware that there are cases where a build up of ammonia and ammonia-scented sweat (and urine, or breath) can be caused by more serious underlying kidney or liver issues. So, if it’s something that happens to you often, it warrants a visit to the doctor to get yourself checked out.
Adding more carbs to your diet, especially around training sessions – and potentially drinking more fluids – is a good place to start if your regime is a bit light on either of these at the moment.
Always seek medical advice from a doctor if you are concerned about your health
Andy Blow is a Sports Scientist with a BSc Honours degree in Sports and Exercise Science from the University of Bath. An expert in hydration and nutrition, he has co-authored a number of scientific studies and books.
He was once the Team Sports Scientist for the Benetton and Renault Formula 1 teams and remains an adviser to the Porsche Human Performance Centre at Silverstone.
Andy has finished in the top-10 of Ironman and Ironman 70.3 races, as well as winning an XTERRA Age Group World title. It was his own struggles with cramp that led to him specialising in hydration and founding Precision Hydration.
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