Walk through any grocery store or gym lately and you’ll probably see electrolyte drinks, powders and tablets on the shelves. Many promise better hydration, more energy and improved athletic performance. But what exactly are electrolytes, and do most people actually need them?

Electrolytes, like sodium, potassium, calcium, magnesium and chloride, are minerals that help your body work properly. They balance fluids, control muscle contractions, support nerve function and keep your heartbeat steady. Most healthy people get enough of these minerals from what they eat and drink regularly, without needing special drinks or supplements, but there are times when extra electrolytes can be helpful.

Here’s how to know whether you should grab that sports drink or supplement.