Diabetes causes an increase in blood sugar levels. If not controlled, this may cause several complications over time. Some common complications of uncontrolled diabetes include heart diseases like coronary artery disease, diabetic retinopathy (damage to the retina of the eye), and diabetic neuropathy (damage to the nerves). It may also cause diabetic nephropathy (kidney damage), diabetic foot (foot ulcers that may turn gangrenous), and other serious conditions like hearing impairment and severe skin conditions.