Type 1 diabetes is an autoimmune condition, which means that the body is attacking its own cells. In Type 1 diabetes, the cells that create insulin are attacked by the body, so the body is no longer able to produce insulin. Scientists still aren't 100% sure what causes type 1 diabetes. There is thought to be a genetic component, but some people develop Type 1 diabetes without having a relative with the illness. Therefore, scientists also suspect that some form of virus may trigger the autoimmune process of Type 1 diabetes.
One cause of type 1 diabetes is when the body encounters an inability to produce insulin, the hormone which controls the amount of glucose (sugar) in your body. Insulin is usually produced by the pancreas. Type 1 diabetes is an autoimmune condition; your immune system mistakes the cells in your pancreas as harmful and attacks them, destroying them completely or damaging them enough to stop them producing insulin. It is unknown why the immune system may do this, but research has suggested that it may be due to viral infection.
Another cause of type 1 diabetes may purely be genetic, as it is usually inherited.
Diabetes is an autoimmune disease. If a person has the genetic markers to develop an autoimmune disease they have the possibility of developing the disease. When a person develops an illness, their body can mistakingly attack it's own pancreatic cells leading to the development of Type I Diabetes.