Type 1 often affects children and young adults, but it can happen later in life. It can start suddenly, and it tends to worsen quickly.
Risk factors include:
having a family history of diabetes
being born with certain genetic features that affect the way the body produces or uses insulin
some medical conditions, such as cystic fibrosis or hemochromatosis.
In type 2 diabetes, the body's cells start to resist the effects of insulin. In time, the body stops producing enough insulin, so it can no longer use glucose effectively.
This means glucose cannot enter the cells. Instead, it builds up in the blood.
This is called insulin resistance.
It can happen when the person always or often has high blood glucose. When the body's cells are overexposed to insulin, they become less responsive to it, or maybe they no longer respond at all.
Symptoms may take years to appear. People may use medications, diet, and exercise from the early stages to reduce the risk or slow the disease.