I have two clients. Let’s call them Maria and James. Both are runners. Both weigh about 65 kilograms. Both run a half‑marathon in similar conditions. Maria finishes her race glowing, drinks some water, and feels fine. James finishes his race covered in white salt stains, cramps up in the parking lot, and says he feels like he’s been hit by a truck. Same distance. Same pace. Same temperature. Different bodies.
The difference is sweat sodium concentration. Maria loses about 400 milligrams of sodium per liter of sweat. James loses 1,200. That’s three times as much. Over a two‑hour race, Maria might lose 800 milligrams of sodium total. James loses 2,400. James’s body is dumping salt like it’s going out of style, while Maria’s is holding on.
Most people have no idea which category they fall into. They just know that some people cramp and some don’t. Some people get headaches after exercise. Some people crave salt. Some people can drink plain water all day and feel great. It’s not random. It’s genetics.
Your sweat sodium concentration is determined mainly by your CFTR gene. That’s the same gene involved in cystic fibrosis. People with certain variants of this gene have saltier sweat. You can’t train it away. You can’t diet it away. You can’t willpower it away. You can slightly reduce it through heat acclimation, but the baseline is set by your DNA.
So the first step is to figure out where you fall on the salty sweat spectrum. Here are the telltale signs.
If you see white salt rings on your clothes after exercise, you’re salty. If your eyes sting when you sweat, you’re salty. If you can taste salt on your lips after a run, you’re salty. If you crave pickles, salted nuts, or sports drinks after working out, you’re probably salty. If you cramp frequently, especially in hot weather, you’re likely salty.
If you don’t have any of those signs, you might be a light or average sweater. Your sweat is more like diluted water. You can get away with plain water during most workouts. You might not need electrolyte supplements.
James had all the signs. His hats looked like they’d been dipped in powdered sugar. His shirts were stiff with salt. He craved french fries after every run. He cramped during every race longer than 90 minutes. He tried drinking more water. That made it worse. Because plain water was diluting his already low blood sodium. His body was losing salt faster than he was replacing it.
We did a sweat patch test. It cost about $40. The results showed his sweat sodium was 1,180 mg/L. That’s in the 90th percentile. For comparison, the average is around 500‑700 mg/L. Light sweaters can be as low as 200‑300 mg/L. Elite athletes who have heat‑acclimated might drop into the 300‑400 range. James was off the charts.
With that number, we built a plan. Before exercise, he drank 500 mL of water with 500 mg of sodium. That’s a lot of salt — about a quarter teaspoon. During exercise, he took a salt tablet every 30 minutes (300 mg each) and drank a high‑sodium sports drink (500 mg per liter) at a rate of 500 mL per hour. Total sodium per hour = 300 from tablets + 250 from drink = 550 mg. Still less than his loss of 1,180 mg per hour, but enough to keep his blood sodium from crashing. After exercise, he drank another 500 mL of electrolyte solution and ate a salty snack like pretzels or a bagel with salt.
The cramping stopped. He hasn’t cramped in two years. He said it felt like magic. It wasn’t magic. It was matching his intake to his losses.
Maria, the light sweater, did the same sweat patch test. Her result was 340 mg/L. Her sweat rate was about 0.9 L/hour. That’s only 306 mg of sodium lost per hour. She could easily replace that with a sports drink at 500 mL per hour (250 mg sodium) plus her normal diet. She didn’t need salt tablets. She didn’t need a heavy pre‑load. She just needed to drink enough fluid.
The danger for light sweaters is overdoing sodium. If you take salt tablets when you don’t need them, you can spike your blood sodium and cause bloating, high blood pressure, or even nausea. Don’t assume you’re salty just because you sweat. Sweat volume is different from sweat sodium.
I had a client once who heard that salt tablets helped with cramps. He started taking them during his 5‑k runs. He didn’t cramp before, and he didn’t cramp after, but he did get a splitting headache and felt puffy. His sweat sodium was average. He didn’t need the tablets. The extra sodium was just sitting in his system, pulling water into his blood vessels and raising his pressure.
So how do you know without a sweat patch? The salt stain test is free. After your next hard workout, let your shirt dry. If you see white rings, you’re likely a salty sweater. If you don’t, you might be average or light. The stinging eyes test is also free. Next time you sweat, let a drop roll into your eye. If it burns like crazy, that’s sodium. If it just feels like water, you’re less salty.
The craving test is another clue. After exercise, do you crave salt? Do you reach for chips, pickles, or salted nuts? That’s your body asking for replacement. Light sweaters usually don’t crave salt. They crave water.
The cramping test is the most practical. If you cramp during or after exercise, especially in hot weather, you’re likely losing a lot of sodium. Try adding 500 mg of sodium before your next workout and see if it helps. If it does, you’re salty.
One more factor: heat acclimation. When you first start exercising in a hot climate, your sweat sodium is higher. Over two weeks of regular exposure, your body learns to conserve sodium. Your sweat becomes more dilute. So if you’re new to Miami or Phoenix, you might be temporarily saltier than you will be after acclimation. James had been training in Texas for years, so his 1,180 mg/L was his baseline. He wasn’t going to get lower without moving to Alaska.
Sweat rate also matters. A person with moderate sweat sodium (700 mg/L) but high sweat rate (2 L/hour) loses 1,400 mg per hour. That’s the same total loss as a salty sweater with a lower sweat rate. So both factors matter. My friend Dave from the earlier article had moderate sodium but high sweat rate. He still needed salt tablets because his total loss was high.
The tool I built for sweat sodium helps you estimate your category without a patch.
Exercise Sweat Loss Estimator
Includes a sodium concentration questionnaire based on salt stains, stinging eyes, and cramping history. Estimates your mg/L loss.
All data stays in your browser — we never see it.
Beverage Hydration Index Tool
Filter drinks by sodium content. Find the ones that match your sweat profile.
All data stays in your browser — we never see it.
Daily Water Intake Calculator
Sodium replacement is only part of the picture. Don’t forget total fluid.
All data stays in your browser — we never see it.
