The Role of the Skin in Regulating Body Temperature and Fluid Balance

The skin is the largest and heaviest organ of the body. The skin is responsible for keeping your body safe from trauma, regulating the body temperature, maintaining fluid and electrolyte balance, as well as sensing pleasant and painful stimuli. The skin is also responsible for ensuring that many vital chemicals and nutrients remain inside the body as it provides a barrier against harmful substances from entering the body while shielding the body from the harmful effects of ultraviolet radiation from the sun. In addition to this, the skin’s color, texture, and various folds are also what separate people out as individuals.^(1, 2, 3)

The skin has a critical role to play in the process of thermoregulation or controlling the temperature of the body. The skin is a part of the integumentary system, which also comprises of hair, nails, and glands. The ability of an organism to regulate its body temperature within certain set boundaries, no matter what the surrounding temperature is, is known as thermoregulation. This is part of homeostasis, which is a dynamic state of stability that is achieved between the internal and external environment. The skin plays an important role in achieving homeostasis, keeping the various aspects of the body constant, especially temperature. It carries out this function by reacting in different ways to both cold and hot conditions to ensure that the inner body temperature is kept at a more or less constant level.^(4, 5)

Owing to the location of the skin, it acts as the perfect barrier to the environment and our interior body organs. Due to its very large surface area, the skin is able to play a vital role in the process of thermoregulation. In a healthy person, if all other factors are taken to be equal, the body keeps on constantly generating heat due to the wide variety of physical and metabolic processes that continue happening. When the body is at rest, a person is expected to have a higher body temperature by 1 degree Celsius every five minutes due to these processes. If, however, this temperature rise is allowed to go on unchecked, it can kill a person rather quickly. This is where the skin’s thermoregulation comes into play.⁽⁶⁾

The process of skin-based regulation of the body temperature takes place in various ways. The first way is because of the presence of abundant blood vessels in the dermis layer of the skin, the middle layer. If the body needs to cool down, the body immediately starts to vasodilate these blood vessels in the dermis layer.⁽⁷⁾

1. Vasodilation

   Vasodilation is a term used to refer to the process of expansion of the size of the blood vessels. Once these peripheral blood vessels of the skin have become enlarged, it allows for a greater amount of blood to start flowing to the surface of the skin. This lets the body release a lot of the body heat through the process of radiation. Radiation, in this particular case, means thermal radiation, which is the process of transferring heat through space through the use of electromagnetic waves.^(8, 9)

2. Convection

   On the other hand, if circulating air or water in a pool comes in contact with your skin when you are feeling very hot, this will lead to heat loss by the process of convection. In convection, the higher the amount of the body’s surface area that is exposed to the circulating air or water, the higher will be the speed of the circulating air or water, and the smaller the distance between the skin’s surface and the dermis layer’s blood vessels, the greater will be the heat lost from the body through the process of convection.

3. Conduction

   The process of conduction also has a role to play in thermoregulation. For instance, if your skin touches a cold object, then the body will lose heat through the process of conduction. Conduction is the direct transfer of heat from a hotter surface to a colder surface that is touching that hot surface.⁽¹⁰⁾

4. Perspiration

   The body further regulates its temperature through the process of perspiration or sweating. Generally speaking, the process of sweating starts when the temperature of the body goes above 37 degrees Celsius. The production of sweat is increased or decreased as required. For example, if we feel the need to cool down, the body will increase the production of sweat. As the drops of sweat form on the skin and then evaporate from the surface of the skin, they take away the body heat with them. The greater the surface area of the skin, the higher the sweating rate, and the greater the rate of cooling through the process of sweating.^(11, 12)

   When you look at the loss of body heat, the processes of convection and radiation are known to be highly effective when the environmental temperature is below 20 degrees Celsius. At the same time, evaporative cooling accounts for the maximum loss of heat once the environmental temperature goes above 20 degrees Celsius, especially when it gets hotter than 35 degrees Celsius. Greater humidity, though, restricts the ability of the body to get rid of the heat through sweating.

5. Role of the Arrector Pili Muscles

   Another role in the thermoregulation process is also played by the hairs present on the skin. These hairs usually lie flat on the skin, preventing the heat from getting trapped by the layer of still air present between the hairs. This happens through the tiny muscles located underneath the surfaces of the skin. These tiny muscles are known as arrector pili muscles.

   Once these muscles relax, the attached hair follicles do not stand up and they lie flat. These flat hairs boost the flow of air next to the skin and also increase the loss of body heat through the process of convection. However, the exact role this process plays in keeping the body cool remains widely debated among researchers.⁽¹³⁾

   At the same time, if the body needs to prevent the loss of excessive body heat, it immediately constricts the blood vessels of the skin. This process is known as vasoconstriction and in this, the blood vessels become narrower than they were before. This causes a lesser amount of blood to flow through the skin, thus allowing lesser heat to escape into the environment. The body also restricts or stops the process of sweating to reduce any evaporative body heat loss.

   Apart from this, the body also thermoregulates by using the hair on the skin. The arrector pili muscles contract and lift up the hair follicles. This causes the hairs to stand up, acting as an insulating layer that traps the body heat. This is how goosebumps get created.

Apart from thermoregulation, the skin is also responsible for regulating water movement along with proteins, fats, and water-capturing molecules. The skin maintains fluid balance and prevents our body from getting dehydrated. The topmost layer of the epidermis, known as the stratum corneum, has a very important role in preventing our bodies from drying out.

The epidermis is the topmost layer of the skin and the stratum corneum is the outermost layer of the epidermis. The stratum corneum is made up of 15 to 20 layers of cells known as corneocytes that are embedded inside a flexible fatty matrix. Corneocytes are comprised of a skeleton that is made up of keratin, which is a protein, and a natural moisturizing factor (NMF), which is made up of water and many other smaller molecules.

When the corneocytes cells come in contact with water, they absorb it. The outermost layer of the stratum corneum contains keratin protein packed together tightly to ensure that it does not bind to water well. However, the NMF in these cells is able to latch onto the water molecules. In the middle layer of the stratum corneum, the keratin gets unfolded, providing space for the water molecules. As the water molecules move into this later, they push apart the keratin, thus making more space for more water molecules. This is what gives the skin a sponge-like capacity to absorb moisture and remain elastic.^{(14, 15, 16)}

This combination of keratin and NMF allows the corneocytes cells to expand, but remain mobile while being embedded in the fat of the skin. As a result of this, our skin remains soft and elastic or pliable and also controls the ability of water molecules to pass through the stratum corneum into or out of the body. The fats that are found outside the corneocytes also restrict the movement of water and prevent the NMF from getting out of the cells, which may reduce the ability of these cells to absorb water.

By changing the ability to absorb water looking at the amount of water available, the skin maintains its own flexibility and also protects the body from dehydration or swelling up due to excess water.

The skin is the outermost layer of the human body and it serves as the first line of defense against harmful particles. Being the largest organ of the body, the skin plays many critical roles, including regulating the body’s temperature and maintaining fluid balance in the body. Taking good care of your skin by eating a well-balanced and nutritious diet and drinking plenty of water will ensure that the organ is able to continue carrying out the many roles it has to play.

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