Sweat or perspiration is the body’s way to cool itself. We tend to sweat more when we are hot and less when are feeling cold. Most people see sweating as an uncomfortable and undesirable process but it is actually a life saving mechanism. Sweating excessively is one of the more commonly known abnormalities with perspiration. It is often a cause of great distress. On the other hand, sweating too little or even not at all especially in hot environments can be dangerous and even fatal.
What is anhidrosis?
Anhidrosis is the medical term for no sweating. This means that a person is unable to perspire as would be normally expected. A similar term is hypohidrosis. This means that the sweating is at very low levels as would be the norm for the situation. Disturbance in sweating in this way allows the body temperature to rise and eventually lead to heat-related illnesses. In hot environments, this can be fatal within hours or days. Anhidrosis is usually a consequence of some underlying problem or disease which needs to first be treated for sweating to be restored. Patients with certain causes of anhidrosis may never be able to sweat as normal and have to adapt their lifestyle to avoiding heat and keeping cool through artificial methods.
There can be several reasons why anhidrosis or hypohidrosis occurs. For normal sweating to occur, the following processes are necessary :
- The temperature control center must be able to detect that the temperature is too high.
- Nerves must carry stimulatory signals from the temperature control center to the sweat glands.
- The sweat glands must be able to produce and secrete sweat.
- There must be sufficient water available for sweat production.
Therefore anhidrosis is mainly a problem with the temperature control centers in the brain, the nerves that control sweat glands, a defect with the sweat glands or insufficient water availability in the body. This entire system of regulating temperature and controlling sweating is not under voluntary control.
When the body temperature is rising above the normal range, certain mechanisms have to take effect to cool it down. The blood vessels in the skin widens (dilates). More blood flows to the skin surface and heat can pass out into the environment. Sweating makes this heat dissipation more effective because when sweat evaporates from the skin surface, it carries away more heat.
When it is cold and the body temperature is at risk of falling below the normal range then the opposite occurs. The blood vessels narrow (constrict). Less blood flows through the skin surface and therefore less heat is lost to the environment. Sweating diminishes and even stops altogether as it is not needed for dissipating heat.
The fine hairs on the skin surface also play a role in temperature control. When it is cold these hairs stand upright. It slows down the flow of air over the skin which limits heat loss. It is seen as “goose bumps” or “goose flesh”. When it is cold, these hairs lie flat thereby allowing air to move easily over the skin surface and carry away any heat.
The temperature control center (thermoregulatory center) in the brain has temperature sensitive nerve cells. When it detects that the body temperature is higher than normal then it triggers the autonomic system. Signals are sent to the eccrine sweat glands in the skin to begin releasing sweat onto the skin surface. The degree of sweating correlates with the extent to which a person’s body temperature is elevated above the norm. It also depends on how quickly the heat is being lost into the environment.
Picture from Wikimedia Commons
Sweating reduces or even ceases in cold environments or when the body’s temperature dips below normal. This is a result of the thermoregulatory center sending fewer stimulating signals to the sweat glands and other processes that inhibit sweat production and secretion. This entire process is controlled by the autonomic nervous system. In other words it is not under voluntary control although certain thoughts, memories and emotions can trigger sweating.
No Sweating Causes
There are number of diseases and medical conditions that can lead to anhidrosis. One of the physiological causes is age. The normal temperature control mechanism in elderly people may be impaired so cooling measures are not started when needed.
Damage to the temperature centers in the brain (hypothalamus), spinal cords that carry the nerves and nerves out of the spinal cord (peripheral nerves) can affect normal sweat control. It may be seen in conditions such as :
- Diabetes mellitus (diabetic neuropathy)
- Horner syndrome
- Hypothalamic dysfunction, injury or tumor
- Lung cancer, small cell
- Multiple system atrophy
- Parkinson’s disease
- Ross syndrome
- Sjogren’s syndrome
- Spinal cord injury
- Spinal cord meningiona
- Sympathectomy (surgery)
The sweat glands and even the nerve endings controlling it may be damaged or destroyed with certain skin problems. Sometimes blockage of the sweat ducts prevents the sweat from being secreted onto the skin surface. This may be seen in :
- Miliaria (prickly heat)
- Radiation damage to the skin
- Various severe skin diseases
Picture of heat rash (miliaria) from Dermatology Atlas (Brazil) courtesy of Samuel Freire da Silva, M.D.
Metabolic disorders are any disruptions in the body’s chemical reactions. It may be a result of problems with nutrients, hormones, enzymes, electrolytes or the presence of toxic compounds. This affects a number of different processes in the body and sometimes temperature control and sweating is affected.
- Diabetic coma
- Fabry disease
Certain drugs may affect the normal sweating mechanism in some people. The types of drugs that may be involved includes :
- Muscle relaxants
- Tricyclic antidepressants
Some of these drugs are used to treat excessive sweating or conditions like anxiety which can lead to excessive perspiration. Overuse of these drugs are more likely to lead to anhidrosis.
Genetic problems may affect the normal functioning of sweat glands or sometimes there may be very few sweat glands. This may be seen with conditions like ectodermal dysplasia.
The main symptom is deficient or absent sweating. This can occur throughout the body (generalized), in a certain area only (localized) or scattered areas (diffuse). When the absent sweating is localized or diffuse, it is not uncommon for neighboring regions with normal sweating function to start sweating excessively in an attempt to compensate.
The lack of sweating allows for the body temperature to rise. The symptoms of heat-related illness may therefore also be present :
- Skin redness (flushing) or sometimes paleness
- Muscle cramps
- Muscle weakness
- High body temperature
When anhidrosis occurs due to dehydration or if there is excessive sweating in neighboring parts leading to dehydration then there may also be other symptoms present such as :
- Changes in pulse and blood pressure
Patient’s will report not sweating sufficiently or at all and some of the heat and dehydration symptoms may be evident on very hot days. These are not conclusive indicators of anhidrosis. Further investigation is required if anhidrosis is suspected. These includes tests to stimulate sweating and confirm its presence as well as to assess and measure the distribution of sweating. A skin biopsy may also be necessary in some cases.
The tests can confirm the absent of deficient sweating but does not indicate the cause. Further testing for the causative diseases mentioned above will need to be conducted. A patient’s medical history and a thorough clinical examination may provide a better indication of the possible causes. However, no cause may be found in some instances.
The aim of treatment is to treat the cause of anhidrosis. Measures to cool the body should be implemented immediately. This includes :
- Resting in a cool environment.
- Drinking sufficient water and preferably oral rehydrating solutions which contain electrolytes.
- Removing as much clothing as possible.
- Moistening the skin with cool or cold water.
There is no specific preventative measures for anhidrosis. Seeking medical treatment at an early stage for the causative condition can possibly prevent anhidrosis from ever starting up. Once it develops, the only preventative measures are aimed at preventing excessive body heat and heat-related illnesses. Patients with anhydrosis or hypohidrosis should therefore consider the following :
- Wear light-colored and thin clothing.
- Use water sprays over the skin on very hot days.
- Try to stay indoors in air conditioning.
- Avoid excessive physical activity especially when outdoors on hot days.
- Seek immediate medical attention at the first signs of heat-related illness.