Pancreatic cell damage is the cause of diabetes.
People with type 1 diabetes have immune systems that attack the insulin-producing cells in their pancreas for reasons that remain a scientific mystery. As a result, the cells are unable to produce insulin, which is necessary for other cells to access the bloodstream's glucose for energy. The bloodstream then becomes unhealthyly high in sugar. Conversely, those who have type 2 diabetes can still produce some insulin, but not enough. As a result of their cells developing insulin resistance (often as a result of obesity), glucose builds up in the bloodstream.