Diabetic sores have a variety of causes, the most common of which are dry skin and diabetic nerve damage, according to WebMD. Other causes of skin sores are external injuries, bacterial, yeast and fungal infections.
The lack of insulin and increased blood glucose levels in diabetics causes skin to lose water and become dry, cracked and sore, states WebMD. Diabetic neuropathy — nerve damage that usually affects the feet and the legs — often results in loss of nerve impulses that help keep the skin hydrated, supple and moist. This condition can cause cracking of the soles and itchy sores. These sores can also develop into diabetic blisters that heal faster when the blood sugar is lowered through a combination of diet, exercise and medication.
Increased glucose in the blood can trigger yeast and fungal infections that cause blisters, itching and sores, states the American Diabetes Association. The lack of insulin impairs the body's ability to heal wounds. Consequently, bacterial infections such as Staphylococcus and fungal infections such as Candidiasis are far more common in diabetics. The infection of hair follicles, joint stiffness and digital sclerosis are other infections that affect diabetics. Skin allergies are aggravated by Type II diabetes, making common rashes and bumps painful and slow to heal.