eccrine glands

What Are Eccrine Glands?

Eccrine glands are one of two types of sweat glands in the human body. Found throughout the skin but in highest concentration on the palms, soles, and forehead, eccrine glands are responsible for the electrodermal activity (EDA) that is one of the three core channels measured by the polygraph. They are the biological transducers converting autonomic nervous system commands into the measurable electrical changes at the skin surface.

How Eccrine Glands Produce Electrodermal Responses

Eccrine glands are innervated by sympathetic nerve fibres that are uniquely cholinergic — they use acetylcholine rather than the noradrenaline used by most other sympathetic fibres. When the sympathetic nervous system is activated during the arousal associated with deception, these fibres stimulate eccrine glands to secrete sweat into their ducts. Even before sweat reaches the surface, the filling of ducts with electrolyte-rich fluid reduces skin resistance (or increases skin conductance), producing the electrodermal response the polygraph records.

Palmar Eccrine Glands and Emotional Sweating

Palmar eccrine glands respond primarily to emotional and psychological stimuli rather than thermoregulatory demands. While eccrine glands across the body respond mainly to temperature, the palmar glands are activated by the autonomic nervous system's emotional pathways. This is why the polygraph's electrodermal sensors are placed on the fingers — the palmar eccrine glands provide the most sensitive window into emotional and cognitive arousal.

Density and Individual Variation

Eccrine gland density varies across body sites (approximately 600–700 per cm² on fingertips versus 100–200 on the back) and between individuals. This variation contributes to differences in tonic skin conductance levels between examinees. However, because CQT scoring evaluates differential responsivity within each examinee rather than absolute conductance, these individual differences do not affect scoring validity.

Factors Affecting Eccrine Function

Several factors can affect eccrine function and electrodermal data quality. Anticholinergic medications can suppress gland activity. Dermatological conditions may alter conductance. Ambient temperature and humidity influence baseline sweat production. Very dry skin may indicate reduced activity, while excessively moist palms may produce elevated baselines with reduced dynamic range. Examiners note these factors during the suitability assessment.