Enzymes are complex proteins that cause a specific chemical change in other substances, without being changed themselves. For example, they can change starches, proteins, and sugars into substances the body can use. Blood clotting is another example of enzymes at work.
Enzymes are essential to all bodily functions. They are found in the mouth (saliva), stomach (gastric juice), intestines (pancreatic juice, intestinal juice, and intestinal mucosa), blood, and every other organ and cell in the body.