A hormone is a chemical messenger that travels through your bloodstream to deliver instructions to different parts of your body. Your body produces dozens of different hormones in special organs called glands, and each hormone carries specific messages that tell your cells what to do.

Think of hormones like texts sent from headquarters to field offices. When you're scared, your adrenal glands release a hormone called adrenaline that makes your heart beat faster and gives you extra energy to react quickly. When you're growing taller, your pituitary gland releases growth hormone that tells your bones to get longer. When you eat a meal, your pancreas releases insulin to help your cells absorb sugar from your food for energy.

Hormones control an enormous range of body functions: growth, energy levels, sleep cycles, mood, hunger, and much more. During puberty, hormones cause the major physical changes that transform children into adults. When someone says they're feeling hormonal, they usually mean their emotions feel stronger or more unpredictable than usual, which can happen when hormone levels shift during growth spurts, illness, or stress.

Unlike the nervous system, which sends instant electrical signals, hormones work more slowly, but their effects often last longer. A single hormone release might influence your body for hours or even days.