Secretion is the process by which cells or glands produce and release useful substances into the body. Your body performs dozens of different secretions every day without you even thinking about it. When you eat, your stomach secretes digestive acids to break down food. When you exercise, your skin secretes sweat to cool you down. When you get a cut, your body secretes substances that help form a scab. These substances are also called secretions.

Different glands specialize in different secretions. Your salivary glands secrete saliva to help you chew and digest food. Your tear ducts secrete tears to keep your eyes moist and wash away dust. Your pancreas secretes insulin to help your body use sugar for energy. Some secretions, like saliva and sweat, leave your body. Others, like hormones and insulin, stay inside and travel through your bloodstream to where they're needed.

Scientists distinguish between secretion and excretion: secretion produces useful substances your body needs, while excretion removes waste products your body doesn't need.