Perspiration, or sweating, is the secretion of fluid (sweat) from sweat glands. This word is both a noun and a verb; it can refer to the act of sweating or to the sweat itself. Sweat mostly consists of water, along with minerals, urea, and lactic acid. Only mammals perspire; some, such as humans, other primates, and horses, perspire relatively more than others because they have more sweat glands. Humans have between two and four million sweat glands. Sweating is one way of cooling the body temperature in warm weather or during exercise.
Function of Perspiration
The function of perspiration in humans and in other animals with many sweat glands, like primates and horses, is to thermoregulate the body, which means to maintain an organism’s temperature at a set point no matter what the surrounding environment is like. Perspiration helps keep a mammal cool when it evaporates from the surface of the skin.
In other mammals with fewer sweat glands, perspiration does play a role in thermoregulation, but it is not as major. For example, dogs have some sweat glands on the pads of their feet to help keep them cool, but they mainly regulate their temperature by panting. This cools them off because it allows water to evaporate from their mouth and throat.
In animals like pigs and rhinos, perspiration is inefficient to cool their bodies, so they wallow in mud to keep them cool. Hippos do not have true sweat glands, and must spend a lot of time in water to keep cool and stay hydrated. Similarly, cetaceans (whales, dolphins, and porpoises, which are all closely related to hippos) live in water and do not have sweat glands; they rely on water for thermoregulation.
Types of Sweat Glands
There are two types of sweat glands: eccrine and apocrine. Eccrine sweat glands are very numerous and found all over the body. They secrete sweat that is odorless and mainly made up of water and salt. They are found in the highest numbers on a person’s palms, soles of the feet, and head. Apocrine sweat glands are found only in certain locations on the body, such as the armpits, ear canals, and genitals. Some structures are apocrine sweat glands that have evolved and perform a special function; the mammary glands, which produce milk, and the ceruminous glands, which produce earwax, are two examples. Apocrine glands also produce odorless sweat, but it can develop the characteristic scent of body odor from bacterial decomposition once exposed to the outside of the body. Apocrine sweat glands are sensitive to epinephrine (adrenaline), and this is why humans tend to perspire more during times of fear, pain, stress, or sexual arousal.
Many Asian people have, on average, relatively less body odor than people of other ethnicities because of a variation in the ABCC11 gene. They also tend to have dry earwax instead of wet earwax. Earwax comes from the ceruminous glands, which are modified sweat glands, and this same gene is the cause of differences in both sweat and earwax production.
Hyperhidrosis is the medical term for excessive perspiration. It is also called hidrosis or diaphoresis (although diaphoresis can also refer to normal perspiration). Hyperhidrosis can be primary, which means that it occurs all over the body, is present from birth, and is passed down genetically, or secondary, which refers to hyperhidrosis that is localized to a specific location and acquired later in life due to development of conditions such as a thyroid disorder, diabetes, or menopause. Anxiety may worsen symptoms of primary hyperhidrosis because it activates the sympathetic nervous system, which causes increased perspiration.
Treatment of Hyperhidrosis
Primary hyperhidrosis can be treated by multiple methods. One form of treatment is the use of clinical strength deodorant, which contains a higher percentage of aluminum chloride than regular deodorants do. If clinically prescribed deodorants do not curtail sweating, then several different medical treatments may be tried. One is iontophoresis, which involves placing the hands or feet in water that has a very low electrical current running through it; although this method has successfully treated hyperhidrosis since the 1940s, scientists still do not entirely understand why it works. A class of prescription drugs called anticholinergics can also be taken orally for treatment. These may have some side effects such as constipation, but they can be helpful in relieving hyperhidrosis, especially when taken before a stress-causing event. Botulism toxin (Botox) injections in the affected areas can also help, although these injections can be painful and the effects on hyperhidrosis wear off by nine months after each injection.
As a last resort, for cases of extreme hyperhidrosis that are not aided by other methods, surgery can be performed. This can involve the removal of sweat glands or destruction of some sympathetic nerves. However, this also may have many side effects. Many patients experience increased perspiration in other areas of their body after the surgery, which is usually irreversible. In some cases, the nerves that were removed can regenerate, leading excessive perspiration to reoccur in the region where the surgery was performed.
People with hyperhidrosis can make some lifestyle changes to reduce sweating as well. This can include wearing loose-cut clothing in breathable fabrics like cotton, bathing frequently, and limiting spicy foods, hot beverages, and alcohol.