If you have type 1 diabetes, it means that your body does not make any or enough insulin, and this is a life-long condition. Because the body needs insulin to absorb glucose from the food you eat, the glucose stays in your blood and, if untreated, can cause high blood glucose levels which are dangerous for your health.
Insulin is a hormone (chemical signal) which is released by your pancreas when you eat, helping your body to absorb the glucose. Without insulin, the glucose stays in the bloodstream where it can cause damage.
If too much glucose stays in the blood, it can cause damage to the blood vessels. This means that nerves and organs of the body won’t receive enough blood carrying oxygen and nutrients, and over a long time this can cause problems, such as nerve damage, eye damage and kidney damage.
If you have type 1 diabetes, it is because an "autoimmune reaction" has started to destroy the beta cells (which make insulin) in the pancreas. An autoimmune reaction means that the body attacks its own cells. As a result, the pancreas stops producing insulin.
Type 1 diabetes has a relatively quick onset, meaning that the pancreas stops making insulin over a short period of time, and it is usually diagnosed in childhood.
The treatment for type 1 diabetes is insulin therapy, which is designed to replace the action of the insulin your body would make naturally. Insulin solution is injected into the body using a pen or a pump to help the body deal with the glucose from the food you eat.
The important thing to remember is that maintaining target blood glucose levels is the best way to avoid damage to health later in life.