Hyperhidrosis is a medical disorder that causes excessive sweating (perspiration). It typically affects the armpits, hands or feet. However, it may impact any part of the skin’s surface except for the lips, external ear canal and sex organs, which do not have the capacity to produce sweat.

Sweating is a natural process that helps maintain body temperature, skin hydration and fluid and electrolyte balance. It is regulated by the body’s sympathetic nervous system. People sweat in response to warm temperatures, physical exertion and situations that cause anxiety, anger, embarrassment or fear. However, the excess sweating associated with hyperhidrosis occurs without these triggers. Therefore, patients with hyperhidrosis may sweat even in cool temperatures or during periods of rest.

Hyperhidrosis is believed to be associated with overactive sweat glands. A sweat gland is a tube of cells that secretes sweat through the pores of the skin. The body contains millions of sweat glands, which can be divided into two main types:

• Eccrine glands. Sweat glands which are present at birth and open directly onto the skin’s surface. These are the most abundant sweat glands in the body, and produce the majority of underarm sweat.
  
  
• Apocrine glands. Sweat glands which develop in regions with numerous hair follicles (e.g., scalp, underarms), and are triggered by emotions. Apocrine glands begin to produce sweat following puberty. They have minimal, if any, impact on temperature regulation.
  
  

  

Both types of sweat glands are located in the dermis (middle layer of the skin), and both have the same physical structure. Sweat is produced in a part of the gland that is coiled. When the gland is stimulated, the cells secrete perspiration, which travels from the coiled part of the gland through a long, hollow tube (duct) to an opening (pore) on the outer surface of the skin.

The sweat glands are stimulated by different regions of the brain. For instance, the hypothalamus controls temperature-related (thermal) sweating, which occurs in response to factors such as heat, humidity and physical exertion, whereas the cerebral cortex regulates sweating caused by emotions. 

Hyperhidrosis typically begins in childhood or adolescence. It affects men and women equally. Although hyperhidrosis generally poses no immediate health risks, the condition can have an effect on everyday activities. For instance, patients with sweaty palms may have difficulty grasping objects, and those with underarm-related hyperhidrosis may need to change their clothes frequently throughout the day. The condition can also lead to various skin diseases (e.g., fungal infections, contact dermatitis).

Hyperhidrosis can be a source of embarrassment for many patients, and may have social, professional and emotional ramifications. For these reasons, cases of hyperhidrosis are believed to be underreported. Therefore, the exact incidence of the disorder is not known.