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Why do we sweat?

exercise | March 17, 2020 | Author: Naturopath

exercise

Why do we sweat?

Perspiration, or sweating can occur when the body becomes over-heated as a way of cooling down. This can occur due to environmental heat and exercise. Sweating may also occur form nervous situations, hot and spicy foods. Hyperhidrosis (excessive sweating) is not well understood and can occur in some people.

Perspiration (sweating) is defined as the secretion of fluid by the sweat (sudoriferous) glands. Sweat glands are tubular in shape and located within the skin and subcutaneous tissue found below, with a small opening on the skin surface where fluid is released. The body contains millions of sweat glands.

Sweat is a transparent odourless fluid which consists primarily of water and electrolytes (mainly sodium and chloride), and also potassium, urea, lactate, amino acids, bicarbonate and calcium. Proteins in sweat called immunoglobulins (function as antibodies) and glycoproteins (carbohydrates joined to proteins) perform a range of functions in the body. Sweat is acidic with a pH of between 4 - 6.

 A bit about Sweat Glands

 A bit about Sweat GlandsThere are two types of sweat glands: Eccrine and apocrine.

Eccrine glands are developed during foetal growth and make up about 75% of sweat glands of the body. They are unevenly distributed throughout nearly the entire body, with larger concentrations found in the soles of feet, palms of hands, armpits, forehead and cheeks.

Nervous stimuli – nerve fibres from the sympathetic nervous system (the system which controls involuntary muscles) send signals to eccrine glands through the neurotransmitter – acetylcholine.

Apocrine the other 25% of sweat glands. They are larger, open into hair follicles and occur mainly in the arm pit, the areola of the nipples the perineum (the area located between the anus and genitals), ears and eyelids. It is thought androgens, (testosterone) regulate apocrine glands rather than stimuli. 

These glands increase in size and start functioning after puberty and secrete a thicker solution containing fatty acids (lipids, cholesterol and steroids) and proteins. This secretion has an odour. Sweat that has an odour is due to bacterial action on sweat or from the solution secreted from the apocrine glands.

Apoeccrine sweat glands are a mix of the 2 also found in the body.

Why we perspire?

There are two reasons for perspiration: 

  • Temperature regulation - as a means of cooling the body 
  • Waste removal - sweating aids in the removal of waste psroduct

Temperature regulation (thermoregulation)

Sweat plays an important role in thermoregulation. The more heat there is the greater the sweat produced. Sweating is the primary response of the body to control temperature in response to external heat stimuli. It can occur during awake hours and also during sleep from signals from the hypothalamus located in the brain. The body’s internal temperature is believed to be the primary control of thermoregulation. Heat stimulates the release of acetylcholine from nerve endings in the eccrine glands and catalyse sweat secretions.

Waste removal

A benefit of sweating is the removal of waste material from the body. Heavy metals, toxins, chemicals, BPA (bisphenol A) and PCB eliminated through sweating. Glycoproteins found in sweat can also aid in the removal of bacteria. They do this by preventing bacteria from adhering to epithelial tissue and use a washing action to flush the bacteria out.

Sweating from Exercise

Sweat glands will activate within 8 minutes of exercise (or heat) and humans are able to produce around 1.4 l of sweat /hour when exercising or with heat. The body will decrease sweating as exercise or heat stress decreases – or after 4-6 hours of prolonged heat stress.

Why do we perspireSweating in response to food

This is known as a gustatory response. Chemicals in some foods can stimulate the nerve responses to heat, this results in a body response of sweating.

Capsaicin, the chemical found in chillies and peppers, can cause the body to sweat

When we sweat too much

Hyperhidrosis (non-thermoregulatory sweating)

Pathological sweating with no underlying medical cause is called primary hyperhidrosis and occurs from hyper-responsive nerve pathways. These pathways involve the sympathetic nervous system, the cerebral cortex and the hypothalamus in the brain. In some cases, this may have a partial hereditary cause.

When a disease state causes excessive sweating this is known as secondary hyperhidrosis. Diseases which may result in excess sweating include.

  • Hyper-functioning of the Hypothalamus - Increased thermoregulatory sweating can occur during exercise due to an over functioning hypothalamus.
  • Diabetic hypoglycaemia – low blood sugar
  • Hyperthyroidism – overactive thyroid
  • Menopause – heat, flushing and sweating are due to abnormal hypothalamic thermoregulatory control which results in abnormal vasodilatory response to minor elevations of core body temperature.
  • Obesity – excessive production of sweat is thought to be a compensatory response due to reduced heat loss. This happens due to a thick layer of subcutaneous adipose tissue. Fat keeps us warm.
     
  • Endocarditis (an infection of the inner lining of the heart)
  • Fever of unknown cause
  • Generalized anxiety disorder - Mental stress - Increased mental stress increases stimulation of the sympathetic nervous system resulting in more sweating.
  • Heart attack
  • Heat exhaustion
  • HIV/AIDS
  • Leukemia and Non-Hodgkin’s lymphoma

Sweating Babies

Some babies sweat excessively during their deepest sleep at night. This is often due to an immature thermoregulatory system. Because of this it is important not to over-dress or buddled baby too warmly. Excessive crying and illnesses such as fevers and infections can be other reasons for sweating in baby. More serious continuous sweating can be a sign of congenital heart disease, which needs medical investigation. In any reason for concern carers should seek medical advice.

What about no sweat

When the body doesn’t sweat (hypohydrosis) it is usually due to disorders of the skin and generally considered not to be clinically significant. It may be due to skin injury such as infection, radiation, inflammation or trauma; atrophy of glands from connective tissue disease such as lupus, Sjogren or systemic sclerosis; some medication; diabetic neuropathy and malaria – due to lesions obstructing sweat glands.

What about Body Odour

Body odour is associated with bacteria or in some cases due to certain foods eaten. 

What about Body OdourSweating from eccrine glands is generally odourless as it is nearly 100% water. Odour from these glands can occur due to bacteria degrading keratin softened by eccrine sweat. Keratin is the fibrous protein which makes up your hair, skin and nail. Some foods can cause body odour – garlic, onion, curry and alcohol for example, and some medications – such as penicillin.

Apocrine secretions are rich in lipids, sterile and odorless. What makes them odorful is when they are broken down by bacteria into volatile acids on the surface of the skin.

The problems from sweating

Dehydration - fluid is lost through sweating especially in hot environments or when exercising

The need for frequent showering, changes of clothes and bedding.

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References

https://healthengine.com.au/info/sweating-perspiration

https://www.msdmanuals.com/en-au/professional/dermatologic-disorders/sweating-disorders/introduction-to-sweating-disorders

https://www.mayoclinic.org/symptoms/excessive-sweating/basics/causes/sym-20050780

Menopausal Hot Flashes: A Concise Review https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6459071/

Hyperhidrosis and Obesity https://link.springer.com/chapter/10.1007/978-3-319-89527-7_3

https://pubmed.ncbi.nlm.nih.gov/26903134-monitoring-of-heavy-metal-levels-in-the-major-rivers-and-in-residents-blood-in-zhenjiang-city-china-and-assessment-of-heavy-metal-elimination-via-urine-and-sweat-in-humans/

Human Excretion of Bisphenol A: Blood, Urine, and Sweat (BUS) Study https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3255175/

Biomonitoring and Elimination of Perfluorinated Compounds and Polychlorinated Biphenyls through Perspiration: Blood, Urine, and Sweat Study https://www.hindawi.com/journals/isrn/2013/483832/

Sweating the small stuff: Glycoproteins in human sweat and their unexplored potential for microbial adhesion https://academic.oup.com/glycob/article/26/3/218/2355446

https://sydneynorthneurology.com.au/focal-hyperhidrosis/

Chapter 25 - Interactions between body fluid homeostasis and thermoregulation in humans https://www.sciencedirect.com/science/article/pii/B9780444639127000254?via%3Dihub

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