The sun is hot and you are sweating. Most of us know how it feels to sweat, and when we sweat. This is a normal bodily response to an increase in temperature as the body tries to cool itself down. As sweat evaporates, it has a cooling effect. However, this is not the full story. Sweating may also be involved in skin hydration, microbial defense against skin infections, salt and electrolyte balance, and removal of toxins and metabolic waste products from the body , and is therefore important for our overall health. Read on to learn more about why we sweat, what happens if we sweat more or less than usual, and how genetics is involved in sweating.
- Where does sweat come from?
- What is the composition of sweat?
- Why do we sweat?
- When do we sweat?
- How much do we sweat?
- Hyperhidrosis or excessive sweating
- Symptoms of hyperhidrosis
- Diagnosis of hyperhidrosis
- Treatment for hyperhidrosis
- What causes hyperhidrosis?
- How many people suffer from hyperhidrosis?
- How does hyperhidrosis affect quality of life?
- Reduced or absent sweating
- How does genetics affect sweating?
- Does sweat smell?
- Body odor
Where does sweat come from?
Sweat glands release sweat onto the skin. We have two main types of sweat glands: eccrine sweat glands that cover most of the body and open directly onto the skin, and apocrine sweat glands that are found where there are many hair follicles, such as armpits, groin and head. A third type of sweat gland, apoeccrine sweat gland, is found mainly in the armpit region.
Eccrine sweat glands respond to increases in core body temperature by releasing sweat on to the skin to cool the body down. There are several million of them in total over the entire surface of the human body, and the number does not change throughout our lives. They are responsible for most of our sweat. Unlike eccrine skin glands, which are active from an early age, apocrine skin glands are activated in puberty .
What is the composition of sweat?
Sweat from eccrine sweat glands is composed largely of water and sodium chloride. Sweat from apocrine sweat glands contains fats, protein, sugars and ammonia .
Why do we sweat?
The main role of sweating is temperature regulation and cooling.
Other functions are:
- Microbial defense against skin infections due to excretion of antimicrobial substances in sweat
- Maintaining salt and electrolyte balance in the cells
- Maintaining surface skin hydration
- Potential role in removing toxins and metabolic waste products 
When do we sweat?
Generally, we expect to sweat more in summer than in winter because the temperature is warmer, but you will sweat anytime your body needs to cool down. Other times you may find yourself sweating are:
- When exercising
- When drinking coffee
- When eating spicy food
- When drinking alcohol
- When smoking
- When you are angry
- When you are under stress, anxious or nervous
- When you have a fever or are ill
- When taking certain medication
- During pregnancy
- During menopause 
How much do we sweat?
The amount of sweat released by the sweat glands varies between people due to the rate of sweat secretion rate per gland. If the sweat secretion rate increases, you will feel like you are sweating more. Many of the factors listed above can influence sweat secretion rate, and it may decrease with age .
Average sweat rates during physical activity show wide variation and depend on factors such as age, gender, weight, environment and clothing, and activity. Sweat rates of between 0.5 to 2.0 liters per hour have been recorded during various sports .
Hyperhidrosis or excessive sweating
While sweating is a normal body function, excessive sweating, called hyperhidrosis, is a condition caused by overactive sweat glands that produce more sweat than is necessary .
There are several types of hyperhidrosis.
The most common type of hyperhidrosis, focal (or primary) hyperhidrosis often starts before age 25 and is associated with increased sweating in certain regions such as armpits, lower back, hands, feet and head .
Generalized or secondary hyperhidrosis
Excessive sweating that affects the whole body is called generalized hyperhidrosis and is most commonly seen in adults. In many cases, this type of hyperhidrosis is caused by an underlying condition and is called secondary hyperhidrosis or diaphoresis. Underlying causes of secondary hyperhidrosis include [4, 5, 6].
- Adrenal gland tumor (pheochromocytoma)
- Anaphylaxis (severe allergic reaction)
- Cancer (e.g., Hodgkin disease, leukemia, bone cancer)
- Carcinoid tumor
- Certain drugs and substances (e.g., some antidepressants, hormone medications)
- Diabetes (sign of low blood sugar, hypoglycemia)
- Heart failure
- Infections (e.g., tuberculosis)
- Overactive thyroid (hyperthyroidism)
- Lung disease
- Parkinson disease
- Pituitary gland tumor (acromegaly)
- Spinal cord injury
- Withdrawal from drugs or alcohol
Asymmetrical hyperhidrosis, or sweating on one-side of the body, has also been described. It is usually an indication for secondary hyperhidrosis, possibly with a neurological cause. Horner and Harlequin syndromes show one-sided sweating. Asymmetrical hyperhidrosis may be accompanied by increased sweating on the other side of the body, called compensatory hyperhidrosis .
Night sweats (excessive sweating at night) are a common feature of menopause and perimenopause. Other underlying medical causes include anxiety disorders, hyperthyroidism or an infection. Some medications including cancer treatments, as well as alcohol consumption and drug use can also cause night sweats .
Symptoms of hyperhidrosis
The excessive sweating that characterizes hyperhidrosis can cause sweat to accumulate and be visible to observers in the form of damp patches on clothes or beads of sweat collecting on the skin. This can cause anxiety and distress to sufferers who may feel they need to change their clothes frequently. Sweat can also irritate the skin causing inflammation and infections, itching, discoloration, cracks or wrinkles; skin on the soles of the feet may disintegrate causing the skin to look as though it is peeling. Furthermore, when sweat mixes with the bacteria of the skin, it produces body odor .
Diagnosis of hyperhidrosis
Diagnosis starts with an assessment of symptoms and medical history followed by tests to assess the amount of sweat or rule out secondary causes.
The following criteria can point to a diagnosis of focal hyperhidrosis
- Excessive sweating typically involving armpits lower back, hands, feet and head for at least 6 months
- Sweating on both sides of the body
- Under 25 years of age
- Sweating disrupting daily activities
- Positive family history of hyperhidrosis
- No sweating at night
- Occurring at least once a week
- Exclusion of secondary causes 
Treatment for hyperhidrosis
Lifestyle changes, such as frequent showers, wearing loose fitting clothes made of cotton and using strong aluminum-containing antiperspirants are important. Recommendations when the feet are affected include wearing leather shoes and moisture-wicking sport socks, using foot powder to absorb sweat and changing socks or tights regularly.
A physician can prescribe nerve-blocking medication, antidepressants, Botox injections, iontophoresis therapy or microwave therapy, and in rare cases, sweat gland removal or nerve surgery is recommended .
What causes hyperhidrosis?
Focal hyperhidrosis often runs in families and may have a genetic cause; however, there is no known medical cause .
How many people suffer from hyperhidrosis?
The prevalence of focal hyperhidrosis is estimated to be between 3% and 5% of the population in the United States [4, 7, 9]. However, estimates are slightly higher for other countries, and it is believed that the true prevalence is underestimated in many cases, possibly because patients are too embarrassed to seek medical help.
How does hyperhidrosis affect quality of life?
The symptoms of hyperhidrosis can be challenging and can negatively affect a person’s quality of life and mental health. A study of 71 people with hyperhidrosis found that three-quarters of them reported excessive sweating had an impact on their lifestyle, particularly choosing clothes. Hobbies, everyday chores such as housework and shopping, as well as work or career choice were also affected by hyperhidrosis, and challenges were greater for people whose hands were affected by excessive sweating. Participants also reported that social situations, personal relationships and physical contact were challenging or accompanied by feelings of discomfort, which continues into their work or choice of career, and embarrassment, anxiety and low self-esteem were common .
Reduced or absent sweating
Reduced sweating is called hypohidrosis and a complete absence of sweating is called anhidrosis.
Hypohidrosis/anhidrosis has a variety of causes including
- Burns, skin grafts and other skin damage
- Connective tissue disorders, such as systemic scleroderma and Sjogren syndrome
- Drug use
- Nerve damage caused by alcohol
- Nerve damage caused by disease, such as diabetes, Guillain‑Barré syndrome, multiple sclerosis
- Neurological disorders, such as Horner syndrome and Ross syndrome, which affect sweating around the eyes and face, or Harlequin syndrome, which is associated with an absence of sweating on one-side of the face, neck and chest
- Skin conditions that lead to blocked pores, such as heat rash, eczema
- Some genetic disorders including Fabry disease and hypohidrotic ectodermal dysplasia [1, 11, 12, 13]
In extreme cases, anhidrosis can lead to increases in body temperature that can be life-threatening .
How does genetics affect sweating?
Certain genetic disorders (Fabry disease, hypohidrotic ectodermal dysplasia) have hypohidrosis or anhidrosis as a symptom. Furthermore, genetics can also change or limit body odor, which is particularly important when you sweat.
Fabry disease is a rare, inherited disorder in which a type of fat called glycosphingolipid builds up in blood vessels and tissues. This leads to symptoms including
- Acroparesthesia: episodes of severe burning pain in the hands and feet that last hours to days
- Anhidrosis or hypohidrosis
- Angiokeratomas: dark red or purple spots on the skin that may be flat or raised and are common on the lower trunk and thighs
- Corneal dystrophy: cloudiness in the cornea that do not affect vision. There may also be changes to blood vessels in the eyes.
- Gastrointestinal problems: abdominal pain, constipation and diarrhea
- Tinnitus: ringing in the ears (tinnitus) or hearing loss
- Lymphedema: swelling in feet and legs
- Fatigue, weakness and body aches
- Dizziness and headache
- Nausea and vomiting
- Delayed puberty
- Heat intolerance
There can also be life-threatening complications including
- Kidney failure
- Peripheral neuropathy: nerve damage
- Heart failure
- Stroke 
There are two main Fabry disease phenotypes (how the disease presents): type 1 is classic Fabry disease and type 2 late-onset Fabry disease. The onset, combination and severity of symptoms vary between those with Fabry syndrome, and also according to the phenotype.
Fabry disease is caused by genetic changes (called mutations or variants) in the alpha-galactosidase A (GLA) gene, which provides the instructions for making the enzyme alpha‑galactosidase A. As a result, the enzyme does not work as it should or is even absent and disease symptoms develop. Fabry disease is inherited in an X-linked manner due to the location of the GLA gene on the X chromosome. As men only have one X chromosome, they only need to inherit one copy of the variant to have the disease. Women have two X chromosomes, and the unaltered gene will often mask the effect of the variant, leading to milder symptoms of the disease. Read our infographic for more information on X-linked inheritance. Newborn screening and carrier screening for asymptomatic individuals can test for variants in the GLA gene .
Hypohidrotic ectodermal dysplasia
People with the genetic disorder hypohidrotic ectodermal dysplasia have fewer sweat glands or sweat glands that do not function correctly and therefore a reduced amount or absence of sweating. Other symptoms include
- Distinct facial features
- Malformed teeth
- Sparse body and scalp hair
It is usually caused by genetic variants in the EDA gene located on the X chromosome and inherited in an X-linked manner. It is also caused by variants in the EDAR, EDARADD or WNT10A genes, in which case inheritance is autosomal dominant or recessive. EDA, EDAR and EDARADD provide the instructions for particular cell layers that interact to form skin, hair, teeth, nails and sweat glands. WNT10A is important for development of the teeth. A genetic change results in impaired development of sweat glands, skin, hair, teeth and nails . Carrier screening can identify variants in the EDA gene.
Trimethylaminuria, also called “fish odor syndrome”, is a rare metabolic disorder. The only symptom is an unpleasant rotten fish odor that can be detected in sweat, breath and urine.
Trimethylamine, which has an unpleasant smell, is formed in the gut when bacteria breakdown food. Usually, the enzyme flavin‑containing monooxygenase 3 helps convert trimethylamine to an odor-free product. Trimethylaminuria is caused by changes in the FMO3 gene that alter the amount or activity of the enzyme so that trimethylamine is no longer broken down.
Inheritance of trimethylaminuria is autosomal recessive, which means a person needs to inherit copies of the variant gene from both parents to develop the disease. A person who inherits one copy of the variant is a carrier and can pass it on to future offspring. .
Does sweat smell?
Although you may think that your sweat smells, in most cases it does not. Sweat is odorless until it mixes with the bacteria on your skin. The type of bacteria, and how they interact with the sweat, influences the formation of body odor. Our diet, hygiene practices, hormone changes, medical conditions and medications can all alter our body odor .
The gene ABCC11 has been associated with type of earwax (wet or dry), sweat excretion by apocrine sweat glands, and the formation of armpit odor. Analysis of armpit sweat samples in a small study found that an absence of certain compounds results in less body odor. The study showed that a single nucleotide polymorphism in the ABCC11 gene that is known to cause the dry type of earwax was responsible for the loss of odor forming components in armpit sweat. The wet type of earwax is prevalent in European populations, while Asian populations are more likely to carry the polymorphism that leads to dry earwax and loss of odor forming components in armpit sweat . However, it has been suggested that this polymorphism alone is not enough to determine the amount or type of body odor, but that ethnicity also plays a role .
The primary role of sweating is to cool the body, such as when we exercise or eat spicy food. It is important to drink water to replace fluid lost via sweat to maintain proper body functions, and the amount you need to drink is determined in part by how much you sweat.
Although sweating is a normal and essential body function, hyperhidrosis sufferers sweat more than the amount considered normal. The cause is probably genetic, but it may also be due to an underlying condition, hormonal changes or medication. Hyperhidrosis can be challenging and embarrassing for patients, and can negatively affect both quality of life and mental health. People with hyperhidrosis may require both medical and emotional support, and a healthcare provider can give advice on the available treatment options.
The content of this article is for informational purposes and is not intended to replace medical advice. Please visit your healthcare provider if you have concerns about your health and well-being.
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