PROLOGUE
The sweat glands are divided into two classes:
- Eccrine, and
- Apocrine gland.
The eccrine glands are the major sweat glands in the body and are generally found throughout the surface. The glands present on palms and soles do not respond to temperature but secrete at the time of emotional stress. The apocrine glands are larger sweat glands and are found in axilla, areola of the nipples, mons pubis, labia majora, ear, eyelid and mammary gland.
The eccrine glands are supplied anatomically by sympathetic fibres, yet they are functionally cholinergic (e.g. pilocarpine increases the flow of sweat and atropine abolishes sweating). The apocrine sweat glands respond to circulating adrenaline (these glands are of sexual significance and remain inactive until puberty).
The daily total amount of sweat secreted by a human is approximately 480-600 ml, which may even rise to 10 litres in extremely hot weather.
TYPES
- Sensible: When sweating is increased and evaporation stopped, drops of sweat appear on skin surface.
SWEATING MAY BE CLASSIFIED INTO (NORMAL PHYSIOLOGICAL RESPONSE)
- Thermal sweating → due to rise of external temperature and is controlled by thermoregulatory centre at hypothalamus.
- Emotional (mental) sweating → chiefly palms, soles and axillae are involved.
- Sweating due to muscular exercise/exertion → factors involved are thermal sweating + emotional sweating.
- Gustatory sweating → eating of spicy food may stimulate sweating in head and neck region.
- Miscellaneous → as a result of sympathetic overactivity, nausea/vomiting, syncopal attack, hypoglycaemia and asphyxia.
COMPOSITION OF HUMAN SWEAT
- A clear colourless fluid
- Specific gravity: 1.001 − 1.006; pH 3.8 to 6.5
- Contains mainly water
- Solid present in sweat are lactic acid, carbolic acid, urea, creatinine, sugar, uric acid, nitrogen and non-protein nitrogen, calcium, iodine, iron, sulphur, copper, amino acids, sodium, chloride, potassium and others
- Sodium: 24-312 mg/dl andChloride: 36-468 mg/dl
HYPERHIDROSIS (GENERALISED)
- Exercise, anxiety, pyrexia, hot climate.
- Thyrotoxicosis, hyperpituitarism, acromegaly, carcinoid syndrome, pheochromocytoma, menopause, pregnancy, obesity.
- Hypoglycaemia.
- Acute myocardial infarction, heart failure, shock.
- Tuberculosis, other infections/pyrogens, lymphoma, malignancy, rheumatoid arthritis.
- Alcohol intoxication, antidepressant drugs, pilocarpine, opiates.
- Intense pain, syncope.
- Rickets, infantile scurvy.
LOCALISED HYPERHIDROSIS
- Organic neurological lesions–brain tumour, spinal cord injury (may help to localise site of lesion), syringomyelia.
- Localised sweating of palms, soles and axillae–hot weather, anxiety, psychoneurosis and embarrassment.
- Dermatological disorders–dyshidrotic eczema, vitiligo, epidermolysis bullosa, palmo-plantar keratoderma, nail-patella syndrome.
- Pachydermoperiostitis (or primary hypertrophic osteoarthropathy with grade IV clubbing + leonine face)–affects skinfolds of forehead and extremities.
- Granulosis rubra nasi–rare genetic disorder; sweating of tip of the nose with a diffuse erythema associated with.
ANHIDROSIS/HYPOHIDROSIS (GENERALISED)
It is less common than hyperhidrosis.
- Heat stroke
- Ectodermal dysplasia
- Scleroderma
- Organic brain damage, especially of the hypothalamus
- Ichthyosis
- Anderson-Fabry's disease
- Miscellaneous: myxoedema, atopic eczema, psoriasis, lichen planus.
ANHIDROSIS/HYPOHIDROSIS (LOCALISED)
- Horner's syndrome (involves half of the face, neck, front and back of upper chest, arm)
- Diabetic or leprosy neuropathy
- ∗ Autonomic neuropathy may lead to anhidrosis and/or gustatory sweating.
COLD AND CLAMMY SKIN
A classical physical finding in shock, and is due to sweating associated with cutaneous vasoconstriction; commonly found in:
- Hypoglycaemia
- Acute myocardial infarction
- Shock and syncopal states
- Alcohol withdrawal
- Dumping syndrome
‘NIGHT SWEATS’ IN CLINICAL MEDICINE
- Tuberculosis
- Lymphoma
- Chronic myeloid leukaemia
- Brucellosis
- Giant cell arteritis
- AIDS
- Nocturnal (sleeping) hypoglycaemia
- Rheumatoid arthritis (rare).
OSMIDROSIS (FOUL SMELLING SWEAT)
The personal body odour is basically determined by apocrine gland secretion. Eccrine sweat is usually odourless.
- Substances excreted in the sweat, e.g. garlic, drugs like dimethyl sulphoxide, arsenic, urea in renal failure (urhidrosis).
- Hyperhidrosis of sole, complicated by bacterial overgrowth may give rise to foul odour in some persons.
- Imaginary foul odour is perceived in paranoid delusion.
- Others (as a result of bacterial overgrowth after sweat excretion): acute rheumatic fever, scurvy, gout, diabetes mellitus, pneumonia, enteric fever.
CHROMHIDROSIS (COLOURED SWEAT)
- Pigment produced by chromogenic bacteria.
- 10% of normal people may have coloured apocrine sweat (yellow/green/blue)–due to the pigment ‘lipofuscins’.
- Drugs excreted through sweat, e.g. rifampicin.
MILIARIA
These are vesicles (sudmina)/papules (prickly heat) resulting from blockage and rupture of sweat ducts. These are commonly seen in tropical conditions of heat and high humidity. The clear vesicles contain sweat and are often found on the trunk during febrile illness (especially, when the body is covered by blanket during pyrexia), and is known as ‘sudaminal rash’.
SWEAT TEST
Pilocarpine iontophoresis test–done to diagnose cystic fibrosis by giving inj. pilocarpine to the patient with measuring the chloride concentration of the sweat → which is very high (> 60 mEq/L) in cystic fibrosis.