The thickening of toenails in diabetic patients may be caused by fungal infections, which is often referred to as “gray nails”. The longer the duration of diabetes, poor glycemic control, the higher the chance of complications, decreased immunity, easy to cause flora imbalance and induce fungal infections, clinically more common is the foot fungal infections, such as the soles of the feet appear dry skin cracking, flaking, thickening of the toenails and so on. Diabetic patients in the combination of other pathogenic infections, may be long-term use of antibiotics, especially broad-spectrum antibiotics are prone to cause flora dysbiosis and decreased resistance to secondary fungal infections increased opportunities. Therefore, diabetic patients with thickened toenails are advised to seek timely medical attention and pay attention to blood sugar control on weekdays.