🧭 When to suspect

Hyperhidrosis is sweating in excess of that needed for thermoregulation, arising from overactive eccrine sweat glands. It is common: primary focal disease affects roughly 1% of the population, and although benign, the impact on work, relationships and mood is frequently profound.

The clinical task in primary care is twofold: separate primary from secondary hyperhidrosis, and never miss a sinister cause. Suspect primary focal hyperhidrosis when there is visible, excessive, focal sweating lasting at least 6 months with no apparent cause, plus at least two of: bilateral and relatively symmetrical; onset before age 25; frequency of at least one episode per week; impairment of daily activities; a positive family history; and cessation during sleep. It typically affects the axillae, palms, soles or craniofacial region. Severity is graded with the Hyperhidrosis Disease Severity Scale (HDSS), a patient-rated 1–4 score in which 3 or 4 denotes severe disease and drives escalation.

Feature	Primary (focal)	Secondary
Distribution	Focal, bilateral & symmetrical (axillae, palms, soles, craniofacial)	Often generalised; may be unilateral or asymmetrical
Onset	Childhood or adolescence, usually before 25	Any age; often new in adulthood
During sleep	Stops during sleep	May persist or wake the patient (night sweats)
Family history	Positive in 30–50%	Usually absent
Other clues	Otherwise well; no systemic features	Weight loss, fever, palpitations, lymphadenopathy, or a drug cause

🧠 Clinical pearl

Whether the sweating stops in sleep is the single most useful discriminator at the bedside. Primary focal hyperhidrosis switches off overnight; drenching sweats that soak the sheets and wake the patient are a different problem and mandate a search for lymphoma, tuberculosis or chronic infection before anything is labelled "primary".

Source: British Association of Dermatologists · British Journal of General Practice

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