It's not possible for injected insulin to work as well as a normal pancreas, so you will have high and low blood sugar levels from time to time.
If your blood sugar stays above your target range for a long time, it can damage many parts of your body .
High blood sugar levels can lead to vision loss and blindness (diabetic retinopathy).
To learn more, see the topic Diabetic Retinopathy.
Having diabetes also puts you at risk for cataracts or glaucoma.
Feet and skin
You may have less feeling in your feet, which means that you can injure your feet and not know it. Common infections from blisters, ingrown toenails, small cuts, or other problems can quickly become more serious when you have diabetes.
If you get serious infections or bone and joint deformities, you may need surgery (even amputation) to treat those problems.
Diabetes: Taking Care of Your Feet
Checklist for Daily Foot Exams
Care of Your Skin When You Have Diabetes
Heart and blood vessels
High blood sugar damages the lining of large blood vessels. This can lead to stroke, heart attack, or peripheral arterial disease.
High blood sugar levels can damage nerves throughout your body. This damage is called diabetic neuropathy. There are three kinds of diabetic neuropathy:
Diabetic peripheral neuropathyDiabetic peripheral neuropathy. This is damage to the nerves that sense pain, touch, hot, and cold. This type of nerve damage can lead to deformities such as Charcot foot . It can also lead to other problems that may require amputation.
Autonomic neuropathyAutonomic neuropathy. This is damage to nerves that control things like your heartbeat, blood pressure, sweating, digestion, urination, and sexual function.
Focal neuropathyFocal neuropathy. Most of the time, this affects just one nerve, usually in the wrist, thigh, or foot. It may also affect the nerves of your back and chest and those that control your eye muscles.
To learn more, see the topic Diabetic Neuropathy.
The kidneys have many tiny blood vessels that filter waste from your blood. High blood sugar can destroy these blood vessels. You won't have any symptoms of kidney damage until the problem is severe. Then you may notice swelling in your feet or legs or all over your body.
To learn more, see the topic Diabetic Nephropathy.