Sweat represents one of the most important factors that help regulate body temperature, and it is a hidden, and sometimes overt, means of communication. Sweat is not one type.
There are two main types of sweat glands that produce sweat with distinct properties. To better understand these properties, scientists are studying the subtleties of the chemical signals found in sweat, the microbes that contribute to body odor, and how sweat is a social signal to others.
Climbing a hill on a warm day causes drops of sweat to pour on the body. The thought of taking a test also makes the palms cold and clammy.
Both cases involve sweating, but the causes and results are different. In one case, the sweating is hot, and in the other, the sweating is cold. What is the difference between them? Is the smell of one stronger than the other?
Doctors from James Cook University in Australia share with The Independent the answer to these questions.
What is hot sweat?
Sweat is the body’s natural response to an increase in its core temperature, which often results from physical exertion.
Hot sweat is also called thermoregulating sweat, because the evaporation of sweat from the skin cools the body and helps prevent its temperature from rising.
The body heats up when exercising or being outside in the sun on a hot day, and then sends a message to the hypothalamus in the brain.
The hypothalamus maintains body temperature within the normal range. So the body sends signals through the spinal cord to peripheral nerves (nerves outside the spinal cord and brain) to reduce heat stress, which in turn stimulates the secretion of sweat from the eccrine sweat glands in the skin.
There are millions of eccrine glands in the body, which are a type of exocrine glands that secrete their substances through ducts to the surface of the body.
The eccrine sweat glands are densely packed in the palms of the hands and soles of the feet, with a density ranging between 250 and 550 glands per square centimeter. It is less dense in areas covered by hair, such as the face, trunk, and limbs.
The sweat produced by the eccrine sweat glands consists mostly of water and salt.
What is cold sweat?
Cold sweat, also called psychological sweat, appears when feeling stressed, anxious, afraid, or in pain.
This feeling activates the amygdala, which is the brain area responsible for feeling and responding to emotions. The amygdala then activates the hypothalamus.
The hypothalamus performs multiple functions at the same time. It sends signals through the spinal cord to the peripheral nerves to stimulate the eccrine sweat glands secreted in the skin.
It also sends a message to the adrenal glands located above the kidneys to secrete the hormones norepinephrine and epinephrine. These hormones travel through the blood and affect the apocrine glands, which are a different type of sweat gland in the skin.
Apocrine glands are mainly found in certain areas of the body, such as the armpits, breasts, face, and genital area. The sweat secreted by the apocrine glands contains a high percentage of fats, proteins, sugars, and ammonia.
Sweat can occur throughout the body, as cold sweat stimulates the eccrine and apocrine sweat glands.
Who has the strongest smell?
Sweat itself does not produce an odor whether it is hot or cold. But it is the volatile organic compounds that result from skin bacteria such as Corynebacterium, Staphylococcus, and Coteibacteria feeding on sweat that produce the odor.
A study in Japan showed that stress, and not exercise as some people think, is what causes unpleasant body odors in people who do not usually have this type of unpleasant odor.
This may be because bacteria prefer the cold sweat produced by the apocrine glands, as it is a nutritious meal rich in fats, proteins, and sugars.
Another study, which analyzed the results of 26 previous studies that included 1,652 people, showed that the body emits specific odors through sweat when feeling afraid, and this proves that fear and stress have distinct odors that warn others.
The terms hot and cold sweat do not express the temperature of the sweat itself, as the secreted fluid (i.e. sweat) is always at body temperature.
The production of hot sweat is natural and an effective response to heat loss from the body, while cold sweat indicates a feeling of malaise.
Sweating has different causes and connotations, and it is recommended to consult a doctor if the sweating is more, less, or different on one side of the body.