The signs of type 2 diabetes are usually subtle, often going unnoticed for many years before a blood test reveals the presence of the disease. The symptoms of diabetes may also be wrongly attributed to obesity or aging, and if not properly treated, may lead to other serious complications including heart disease, kidney failure, blindness, or permanent nerve damage.

The common symptoms of diabetes that occur with both major types of the disease include:

- Excessive urination: Excessive urination, or polyuria, occurs when the body attempts to rid the system of extra glucose through the urine. This condition may then lead to dehydration after losing large amounts of water when excreting the excess sugars.

- Excessive thirst: Excessive thirst, or polydipsia, occurs when the brain receives a signal to dilute the blood in order to deal with the extra glucose. This signal is translated as thirst by the body, which needs to consume more water to counteract the loss by the excessive urination.

- Unexplained weight loss: People with diabetes may experience weight loss even though they are taking in a normal, healthy amount of food, or even an excessive amount, as the disease affects the way the body processes calories. Dehydration and excessive urination are other symptoms that may also contribute to unexplained weight loss.

- Excessive eating: One of the functions of insulin, which is secreted to counter high levels of blood sugar, is to stimulate the appetite. Too much insulin may cause increased hunger and lead to overeating, a condition known as polyphagia.

- Fatigue: Diabetes causes the body to have difficulty processing and using glucose as a means of fuel. To compensate, the body must then work harder to metabolize fat as an alternate source of fuel, which may cause fatigue and a constant feeling of tiredness.

- Slow-healing wounds: Both oxygen and white blood cells are necessary for healing and regenerating new tissue, but when the level of sugar is too high, those cells aren't able to function normally, causing the body to be susceptible to infections and taking longer than usual to heal. Those who have had diabetes for many years may also have poor circulation, which also causes wounds to need more healing time due to a thickening of the blood vessels.

- Frequent infections: Urinary tract infections and both skin and yeast infections are symptoms of diabetes that may be the result of a suppressed immune system. Infections may also be from the extra glucose within the body's tissues, which allows bacteria to grow in excess.

- Blurry vision: While blurred vision isn't technically a symptom that's specific for either type of diabetes, it does occur frequently when blood sugar levels are abnormally high.

- Altered mental state: Symptoms of diabetes, such as confusion, agitation or irritability, may be the result of either very low levels of blood sugar, which is known as hypoglycemia, or from extremely high blood glucose levels, or hyperglycemia.