The main electrolytes lost in sweat are sodium, chloride, and potassium. There are small amounts of other electrolytes present in sweat, such as calcium, magnesium, and phosphate, but their concentrations are usually too low to have any significant effects.
Sweat is mostly water, with small amounts of electrolytes dissolved in it. As sweat evaporates from the skin, it takes the electrolytes with it. This can lead to electrolyte imbalances, particularly if a person is sweating a lot and not replacing the lost fluids.
So it is important to replenish electrolytes by drinking fluids that contain them, such as sports drinks, or by eating foods that are high in electrolytes, such as bananas, coconuts, and leafy green vegetables.
If you're often sweating a lot, such as during intense exercise or in hot weather, it's also a good idea to keep some electrolyte tablets or powder on hand to add to your fluids.