To excrete moisture through the pores of the skin
Children perspire less than adults and require a higher core body temperature to trigger sweating.
Hot flashes cause you to perspire enough to warrant a change of pajamas.
Your heart rate will be up, you will perspire; you will have a headache and stomachache.
You rarely approach people first (even good friends); you prefer to let them come to you and you begin to perspire when they do.
Needless to say, waterproof mascara works well for women who are in the water (swimmers, those who work outdoors in snow or rain) and also for when you perspire a lot, such as during a workout.