Which of the following is a long-term complication of diabetes?

Neuropathy is indeed a long-term complication of diabetes, resulting from prolonged high blood sugar levels that can damage the nerves throughout the body, particularly in the legs and feet. This damage can lead to symptoms such as pain, tingling, and numbness. It's important to note that neuropathy is part of a broader category of complications known as diabetic complications, which include issues related to the eyes, kidneys, and cardiovascular system as well.

In contrast, the other options do not represent long-term complications of diabetes. Cold sores are caused by a viral infection (herpes simplex virus) and are not linked to diabetes. Allergies are immune responses to specific substances and, while they can occur in anyone, they are not complications of diabetes. Tissue swelling, or edema, can occur for various reasons and is not specific to diabetes-related conditions. Thus, neuropathy stands out as a direct consequence of unmanaged diabetes over time, affecting overall health and quality of life.