Insulin is not being produced in the pancreas due to an autoimmune condition attacking its cells. The body's immune system mistakenly attacks the cells responsible for producing insulin in the pancreas, the beta cell, damaging the cells in a way the prevents them from producing more insulin. As more and more cells are damaged, less insulin is produced in the body. This means that more sugar remains in the bloodstream rather than being moved into cells. This high blood sugar causes the symptoms seen in type 1 diabetes.