Sweating on the palm and sole: physiological and clinical relevance.

In mammals, sweating is a multifunctional response that aids in locomotion, thermal regulation, self-protection, and communication of psychological state. Humans possess three types of sweat glands (apocrine, eccrine, and apoeccrine) that are differentially distributed on the body surface and make unique contributions to these distinct functions of the sweating response. In humans, eccrine glands, which are widely distributed on hairy skin, play an important role in thermoregulation. They are also found on the glabrous skin of the palm and sole, where they are not usually activated by heat, but rather by deep respiration, mental stress, and local tactile stimulation. Sweating on the palm and sole, so-called "emotional sweating", acts to prevent slippage while grasping or performing a delicate task using the fingertips. Although the central pathways of emotional sweating are not yet elucidated in detail, it is thought that the amygdala, cingulate cortex, and medulla participate via efferent fibers that descend through the spinal cord and connect to preganglionic sympathetic neurons in the nucleus intermediolateralis. The limbic system, including the amygdala and cingulate cortex, is critical for emotional processing and many cognitive functions. Thus, measurement of sweat output on the palm or sole is useful for evaluating sympathetic function and limbic activity in autonomic and psychiatric disorders.