The main causes of underarm sweating are hyperhidrosis, hyperthyroidism, and increased peripheral nerve sensitivity due to prolonged exposure to high heat, all of which can lead to frequent underarm sweating. Hyperhidrosis is a neurological disorder that tends to cause excessive sweat production in the body. Hyperthyroidism, which tends to increase the amount of thyroid hormones in the peripheral blood of the body, can lead to an increase in the body’s basal metabolic rate, and sweating can occur when the temperature of the body’s skin surface is constantly rising. Prolonged exposure to high heat can easily lead to secretion of tissue fluid through the sweat pores, resulting in sweating. The increased sensitivity of the local peripheral nerves increases the sensitivity to the peripheral environmental temperature, which can also lead to sweating. Sweating caused by the environment requires timely hydration, and sweating caused by disease requires timely symptomatic treatment.