The more severe form of diabetes is type 1, or insulin-dependent diabetes. It’s sometimes called “juvenile” diabetes, because type 1 diabetes usually develops in children and teenagers, though it can develop at any age.
With type 1 diabetes, the body’s immune system attacks part of its own pancreas. Scientists are not sure why. But the immune system mistakenly sees the insulin-producing cells in the pancreas as foreign, and destroys them. This attack is known as "autoimmune" disease.