Swelling of the hands in hot weather may be caused by physiological reasons such as environment and more activities, or it may be caused by pathological factors such as vascular compression of the hands and heart diseases. 1. Physiological reasons: when the weather is hot and no attention is paid to sun protection, the hands are exposed to bright light for a long time, blood vessels will expand locally because of the principle of thermal expansion and contraction, which will be manifested as the symptoms of hand swelling; in addition, more hand activities when the day is hot, which may also cause expansion of blood vessels in the hands and muscle edema. 2. Pathological factors: the blood vessels supplying the hand are compressed due to various reasons, and swelling of the hand may also appear, and due to the hot weather, the distal blood vessels dilate, aggravating the symptoms of poor blood circulation, such as carpal tunnel syndrome, tendon sheath cysts on the inner side of the wrist, and so on. Patients with comorbid heart disease may experience bruising of the circulation due to decreased systolic and diastolic function of the heart, which may also manifest as swelling of the hands. Swelling of the hands in the heat of the day may also have other causes, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.