For many people with diabetes, the thought of using insulin can be frightening. But the reality is, insulin can help you feel better all day.

Insulin is a hormone that's secreted by the pancreas. In a healthy adult, insulin is the chemical key that "unlocks" the body's cells, letting in sugar for energy. Without insulin, cells don't get the fuel they need to grow and function, and high levels of sugar remain in the bloodstream, unused.

People with type 1 diabetes stop manufacturing their own insulin. That's why they need to supply their bodies with insulin from an outside source.

By comparison, people with type 2 diabetes generally still create insulin—they just don't make enough, or their bodies are insulin resistant, meaning their cells are desensitized to the insulin that's available. Sometimes when diet, exercise, and pills aren't able to control their diabetes, people with type 2 may move to insulin therapy on the advice of their doctors. Many people find it's the easiest way of controlling their blood sugar.

When you inject insulin under your skin, it's absorbed into your bloodstream, where it goes to work getting blood sugar into the cells that need it. The time it takes for your insulin to start working depends on the type of insulin you use. Each insulin has its own peak of activity and duration of action.