The hypothalamus (small region of the brain) is responsible for regulating our body temperature. When our core temperature rises above 37°C, our hypothalamus sends signals to our sweat glands to produce sweat. As our sweat evaporates, we cool down. While you're exercising, your body temperature rises, and you produce sweat to cool yourself. Many people think that if they're sweaty they had a better workout but that's not the case. Our bodies sweat to cool us down.
The environment you train in plays a huge role in how much you perspire. You're going to sweat more when you work out in higher temperatures. Completing an exercise class for instance, where the studio owner sets the temperature a bit higher will make you sweat more. That doesn't mean you had a better workout or burned more calories. It means the environment you trained in was warm and your body was cooling you down. If you go for a run outside on a hot afternoon, you're going to sweat more than you would doing the same run on a cool morning. When exercising in hot and humid conditions, it's vital to use common sense. Since sweat cools us as it evaporates, humid conditions can make it easier for the body to overheat.
Fitness fanatics sweat more and sweat earlier on than untrained individuals do. As fitness level improves, the body becomes more efficient at cooling off and perspiration begins at a lower core temperature. Untrained individuals working at the same intensity as a fit person, however, will heat up much more quickly and may sweat more profusely. Those carrying excess body fat also tend to perspire more. It makes the activity being performed more challenging. It also acts as an insulator contributing to higher core temperatures. Men generally tend to sweat more than women do even among those that are trained.
How much an individual sweats varies person to person and depends on many factors including genetics, hydration status, medications, pre-workout/caffeine ingested, stress and anxiety. Sweating more or less than your gym buddy is not a cause for embarrassment. Perspiration is simply a way for our body to stay cool in order to continuing working. Dress appropriately for the training activity and environment by wearing breathable fabrics. Be sure to replenish fluids and stay hydrated.
Above all, train smart and safe and go get your glow on.