Excessive sweating in diabetics is a sign of a significant problem. Excessive sweating is a common symptom of hypoglycaemia, low blood sugar, which left untreated can easily lead to unconsciousness and in some cases diabetic coma. The American Diabetes Association (2009) states "Hypoglycemia happens from time to time to everyone who has diabetes." Therefore, regardless of how well diabetes is controlled, there will be periods of excessive sweating as a matter of course.
The second reason for excessive sweating with diabetes is less common and more dangerous. Diabetes, over time, can damage the autonomic nervous system. This is the portion of the nervous system responsible for involuntary functions such as heart rate, blood pressure, perspiration and digestion. The Mayo Clinic lists diabetes as one of the causes for autonomic neuropathy, the proper name for diseases of the autonomic nervous system. Autonomic neuropathy is not the only type of nerve damage that can be caused by diabetes. There is also peripheral neuropathy, responsible for the tingling, numbness and pain in the extremities, and focal neuropathy, a localised weakness or pain caused by damage to a single or small set of nerves.
Both of these conditions can be controlled through careful control of diabetes. Hypoglycaemia should be treated as soon as the patient becomes aware of it. In fact, the American Diabetes Association (2009) says "when in doubt, treat" to let people know that it is better to do something immediately instead of waiting to see and possibly allowing the situation to progress beyond control. In the case of autonomic neuropathy, the American Diabetes Association (2009) states "if you keep your blood glucose levels on target, you may help prevent or delay nerve damage." Both hypoglycaemia and autonomic neuropathy can be dangerous, but with proper care of their diabetes, patients should be able to keep either condition from becoming a significant problem.