Sweat gland

Function

Eccrine sweat glands are the body's radiators: 2–4 million coiled glands releasing hypotonic saline onto the skin where its evaporation removes heat — sweat rates can exceed 1.5 L per hour during hard exercise in the heat. Cholinergic sympathetic fibres drive them (an exception to the sympathetic norm) — which is why anxiety sweats the palms while heat sweats the trunk.

Apocrine glands, confined to axilla and groin, add scent communication to the system, activated at puberty and metabolised into individual odour signatures.

Blood supply

Dermal capillary network.

Nerve supply

Sympathetic cholinergic fibres (eccrine); adrenergic for apocrine.

Clinical relevance

Hyperhidrosis

Idiopathic over-sweating of palms and soles — botulinum toxin blocks the cholinergic drive for months at a time.

Cystic fibrosis screening

A faulty CFTR chloride channel makes sweat salty — the sweat chloride test confirms cystic fibrosis after a positive newborn blood-spot screen.