TL;DR Don’t choose something with ultra-high amounts of sodium, carbs, or sugar unless it’s necessary based on your exercise levels or a sweat test.

Amy Brownstein, a registered dietitian nutritionist at MyNetDiary, says electrolytes are minerals that exist naturally in the body. These include magnesium, calcium, chloride, sodium, potassium and phosphorus. The role of electrolytes is to help your body rehydrate or stay hydrated by helping your system absorb the water you drink.

Heather Gosnell, a pediatrician, says sodium is the key ingredient for effective rehydration. It also says that a little sugar and carbohydrates help the body absorb water, but drinks high in sugar should be avoided.

Electrolyte powders typically contain these, as well as the aforementioned minerals, which can help with absorption. But how can you know which powder is best for you?

Shelley Balls, RDN, says humans typically lose sodium when they exercise or spend time in high temperatures and that carbohydrates are important to help replenish and preserve muscle glycogen stores to prevent fatigue, especially if they are active for more than 30 minutes. Basically, if you exercise a lot and don’t replenish lost carbohydrates, you will feel fatigued much faster. This is especially true for intense workouts or long sporting events, in which case he recommends increasing carbs again every 30 to 45 minutes. Sugars like glucose have similar purposes and also help replenish muscle glycogen.

If you’re just looking for supplements for everyday use or to calm a hangover brain, you don’t need as high a concentration of sodium or carbohydrates in your electrolyte powder. Brownstein says to choose something within the context of your daily habits and diet. Most people already consume the recommended 2,300 milligrams of sodium per day, he says, so if you’re not depleting sodium stores with intense exercise, you probably don’t need a high-sodium powder. The same also happens with sugar.

The best way to know exactly what you need is to undergo a sweat test, which analyzes the content of your sweat. But if that’s not a medical necessity, your best bet is to choose a powder that falls somewhere in the middle of ingredient concentration—that is, unless you’re sweating a lot, exercising in high temperatures, or training at high altitudes, in which case you should opt for higher concentrations of sodium and sugar. Brownstein adds that if you notice white, chalky residue on your skin or clothing after exercising, you may need to increase your sodium intake.

When it comes to synthetic dyes, Balls says the right answer ultimately comes down to personal choice. Luckily, if you want to avoid these ingredients, many of our recommendations omit them.

To avoid an upset stomach, Balls suggests looking for powders low in magnesium (which can have a laxative effect in large amounts). It also says that because calcium and iron can interfere with each other’s absorption, it’s best to choose a powder that has lower, more balanced amounts of the two supplements. Brownstein says that high sugar and sodium can also upset some people’s stomachs, and that you should read labels to avoid too much supplementation (or too much caffeine). If something contains 100 percent of the daily recommended zinc content, for example, you want to make sure you’re not also taking a multivitamin with the same amount of zinc.

Balls recommends looking for a powder that includes the key electrolytes lost: sodium, potassium, magnesium, and calcium. She says that drinks with artificial sweeteners should be avoided if possible.

Hallie Zwibel, director of the Center for Sports Medicine at the New York Institute of Technology, says: “In addition to causing stomach upset and reducing fluid absorption, repeated consumption of foods and beverages high in sugar can lead to diabetes, as well as possible weight gain.” He adds that “while electrolyte packs can help replenish essential minerals lost through sweat, they should not replace daily water intake.”