Perspiration is the process of fluid removal through sweat glands in the skin. It occurs in response to heat, strenuous exercise or emotional stress. Both the process and the fluid can be called perspiration. It occurs in millions of sweat glands located near the skin surface over almost all of the body. Sweat is carried to the surface of skin by tiny ducts that attach to the pores (tiny holes in the skin).

Sweating is the body’s natural way of regulating its internal temperature. Perspiration is a natural response to feeling hot. When sweat evaporates on the surface of the skin, it removes excess heat and has a cooling effect on the body. Perspiration also removes small amounts of waste products from the body.

A number of factors (e.g., food, medications, illnesses) can affect how much a person sweats and even the way the sweat smells. Sometimes these factors may cause either excessive perspiration (hyperhidrosis) or little or no perspiration (anhidrosis).

Except for causing embarrassment, hyperhidrosis is generally not serious. However, in some circumstances it may be a sign of an underlying health disorder, especially if accompanied by fever.

Anhidrosis can be potentially life threatening. If the body is unable to cool itself naturally by sweating, it can lead to hyperthermia (overheating). If body temperature continues to rise, heatstroke (a severe condition that can lead to shock, brain damage, organ failure and even death) can occur.

Perspiration is the process by which fluid leaves the body through the sweat glands in the skin. This fluid can also be called perspiration, or sweat.  Sweating is the body’s response to heat, strenuous exercise or emotional stress.

According to the American Academy of Dermatology, sweat is 55 to 60 percent fluid, mostly water. Sweat also contains sodium chloride (salt) and tiny amounts of other substances, including potassium, calcium, lactic acid and phosphorus. When these substances exist in fluid they are called electrolytes and help regulate the balance of fluids in the body. Sodium chloride and phosphorus cause sweat to sting the eyes upon contact and also give it its salty taste. Sweat also contains trace amounts of such waste products as ammonia and urea.

Sweat glands are long, coiled, hollow tubes of cells. Millions of sweat glands are located throughout the surface of the body.  The external sex organs, lips and external ear canal are the only areas without sweat glands. The coiled base of sweat glands is located in the second layer of skin (dermis). Sweat is produced in the glands and carried to the surface of skin by tiny ducts that attach to the pores (tiny holes in the skin).

There are two types of sweat-producing glands:

• Eccrine glands. These glands are located throughout the skin, but the highest concentrations are found in the palms of the hands, soles of the feet and forehead. Eccrine glands open directly to the pores in the skin. They are active throughout a person’s life and produce sweat when a person is hot, stressed or feeling strong emotions. Eccrine glands are the most abundant type of sweat gland.
  
  
• Apocrine glands. These sweat glands become active when a person reaches puberty. Apocrine glands connect to the skin through hair follicles. They are located in areas with many hair follicles, concentrated in the underarms and genital region, with some on the scalp and around the nipples. Sweat from apocrine glands is mixed with fatty acids and proteins to produce a thick, oily sweat when a person is under stress or experiencing strong emotions.
  
  

  

Sweat does not have a bad odor. When it reaches the skin, however, sweat interacts with the bacteria normally present on the skin and begins to break down, which can produce an unpleasant odor. Many people use commercial deodorant or antiperspirant products to mask or reduce the smell of underarm perspiration.

Humans depend on the cooling effects of perspiration. Perspiration helps maintain body temperature, skin hydration and fluid and electrolyte balance.

Perspiration is controlled by different regions of the brain. Temperature-related (thermoregulatory) sweating is controlled by the hypothalamus, the part of the brain that controls body functions, such as eating, sleeping and sexual behavior.  Sweating caused by emotions is controlled by the cerebral cortex, the outer layer of the brain. Sweat glands have nerve fibers that enable the brain to control sweating and regulate heat. This reaction is activated when a person’s core (internal) body temperature rises above the normal temperature of 98.6 degrees Fahrenheit (37 degrees Celsius).

Perspiration is the body’s natural way of regulating temperature. When the nerves indicate areas of heat in the body, messages are sent to the sweat glands to produce sweat. Stress or excitement can produce the same messages to the sweat glands to perspire. Sweat moves through ducts to the pores or hair follicles and reaches the skin. When sweat evaporates on the surface of the skin, it removes excess heat and has a cooling effect on the body.

In addition to heat regulation, perspiration has a minor role in waste disposal.  Sweat glands also excrete small amounts of waste products such as urea and ammonia (byproducts of protein metabolism) through perspiration, therefore eliminating them from the body. However, the majority of the body’s wastes are eliminated through the urinary system.

Perspiration is an essential body function and the amount of sweat varies from person to person. The amount of sweat glands a person has directly effects how much they sweat. Although women have more sweat glands then men, men have sweat glands that are more active.

Certain other factors (e.g., heredity, foods, drugs, medical conditions) can also affect how much a person sweats. Sometimes these factors may cause either excessive perspiration (hyperhidrosis) or little or no perspiration (anhidrosis).

Although it can be embarrassing, hyperhidrosis is generally not a cause for concern. Some situations of excessive perspiration are quite common. Hot or alcoholic beverages or spicy foods can make a person sweat more. Some foods may even affect the smell of a person’s sweat. In addition, people with fevers have elevated body temperatures. When a fever breaks and begins to lessen, perspiration can help return the temperature to normal.

If a person suddenly begins to sweat more than usual or if the sweating is accompanied by fever, weight loss, chest pain, shortness of breath or a rapid heartbeat, a patient should seek medical attention immediately. In such cases, hyperhidrosis may be a sign of an underlying illness (e.g., hyperthyroidism). It can also occur as a natural part of the body's processes, such as menopause.

People should also contact their physician when they notice a change in their body odor (e.g., fruity, ammonia-like). Certain changes in body odor may indicate an underlying medical condition.

Lack of perspiration, or anhidrosis, can be potentially life threatening. Some people are born with a rare genetic disorder that results in a lack of sweat glands (ectodermal dysplasia), which causes anhidrosis. These patients require a cooler climate and may require frequent cooling water baths or sprays to maintain a normal body temperature. Other factors that may cause anhidrosis include the use of certain drugs (e.g., antipsychotic medications, diuretics), a severe infection of the sweat glands (hidradenitis) and not drinking enough fluids.

Generally, anhidrosis can severely compromise the body’s ability to cool down and may put a person at risk for hyperthermia (dangerously high body temperature or overheating), especially in hot environments. When a person stops sweating or does not perspire enough to cool the body, the results can be fatal.

Complications of anhidrosis include:

• Heat exhaustion. This often occurs because of excessive exercise and not enough fluid intake (dehydration). The signs and symptoms of heat exhaustion include faintness, nausea, a rapid heartbeat, ashen (pale) appearance and hot, dry skin. A person with these symptoms should cool down immediately by getting into the shade (if outdoors) and drinking tepid fluids. This condition can quickly progress to heatstroke.
  
  
• Heatstroke. A severe condition that can lead to shock, brain damage, organ failure and death. The first signs of heatstroke include severe confusion, bizarre behavior, seizures (sometimes) and coma. A person with this condition requires emergency medical care.

To prevent these complications, it is essential to drink plenty of fluids, particularly water. Fluids containing caffeine, high amounts of sugar, carbonation or alcohol should be avoided or minimized because these liquids tend to have a dehydrating effect on the body.

Keeping hydrated is especially important when exercising, as several quarts of fluid can be lost through perspiration during long periods of vigorous activity. A person should drink fluids before, during and after engaging in exercise to keep the body hydrated. People should also limit outdoor activities to cooler parts of the day (e.g., early morning, early evening) when temperatures are high. Wearing cotton clothing that is loose-fitting and lightly colored can also help people stay cool.  

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following perspiration-related questions:

1. Am I perspiring more than I should be?
   
   
2. Is my excessive sweating a cause for concern?
   
   
3. What can I do to minimize my sweating and body odor?
   
   
4. Under what circumstances should I seek immediate medical attention for excessive sweating?
   
   
5. What foods may be causing me to sweat more?
   
   
6. I rarely sweat, should I be worried?
   
   
7. How can I prevent anhidrosis-related complications?
   
   
8. Will I require surgery for my sweating problems?