Ever notice that when people exercise, some sweat so much they look like they did their run in a pool, while others look as dry as they did before the workout even started? It seems like the more you sweat, the harder you're working, which would also mean more calories burned, but is that the case?
Your body creates sweat to cool you off when your body temperature gets too high. You're born with between two and four million sweat glands, and how much you sweat depends on the number of sweat glands you have (more glands equal more sweat). Women tend to have more sweat glands than men, but men's glands are more active, so they sweat more. Perspiration is also affected by how hot it is, how intensely you're exercising, and whether or not you smoke or drink coffee or cocktails — smoking, caffeine, and alcohol can increase perspiration. What you're wearing also affects your sweat as synthetic fabrics trap in heat. Fat also acts as an insulator, so overweight people sweat more than those of normal weight.
Don't use the amount you sweat as a good indicator as to the number of calories you've burned. What matters is how long and how intensely you're working out. Any weight loss that you experience immediately after a workout is only water weight, and you'll gain it right back as soon as you rehydrate yourself. So don't worry about how sweaty you get. If you go for a 30-minute run and you haven't sweat a drop, you still burned almost 300 calories.