Why do we sweat when in fear?

Fright and fear are emergency states we meet occasionally. In such states the hypothalamus is activated. The result is a wide spread reaction throughout the body called `alarm or stress response'. The stress first excites the sympathetic nervous system, a sub-division of autonomic nervous system of our body.

In such instances the sympathetic nervous system discharges almost as complete unit, a phenomenon called mass discharge. This increases in many different ways the ability of the body to perform vigorous muscle activity.

This stimulation of sympathetic nerves also induces the sweat glands found in the skin all over in our body to secrete large quantity of sweat .

Even though the sympathetic nerve fibres are in general adrenergic fibres (the fibres that secrete adrenal hormone called nor-epinephrine) those fibres innervated to the sweat glands of the skin are cholenergic fibres (fibres that secrete actylcholine as neurohumour) like parasympathetic nerve fibres.

So sweating during fear or any other emergency stress is a sympathetic function. But the normal and primary sweating (sweating during hot and humid weather) is a parasympathetic function, which is also stimulated by the centres in the hypothalamus. However, these parasympathetic nerve fibres are cholenergic fibres.

Source : The Hindu