In summer, especially in periods of heat wave, it is important to stay hydrated and protect yourself from the sun avoiding the effects of high temperatures on our body.

The human body functions optimally between 36 and 37.5 degrees Celsius. But what happens when the body temperature exceeds these limits? How are temperature changes detected?

How the skin detects changes in temperature

External temperature changes are detected in the skin thanks to sensory neurons. These neurons are part of the peripheral nervous system and are classified according to the type of stimulus they detect; in this video you can learn about the different types of sensory neurons that can be found in the skin:

The neurons responsible for detecting temperature are the so-called nociceptive neurons, which are free nerve endings composed mainly of C fibres. These neurons express on their membrane a series of receptors called TRPs that detect temperature at different degrees. In this way, warm temperatures (> 42º Celsius) would be detected by the receptor called TRPV1 [1]. While the colder temperatures would be detected by the TRPM8 (<25º Celsius) and TRPA1 (<17º Celsius) receptors.

In addition to the different temperatures, these TRP channels are known to be the receptors of different molecules that are part of some cosmetic formulations such as mustard oil (TRPA1), menthol (TRPM8) and capsaicin (TRPV1).

Termorreceptores canales TRP

Once the receptors are activated, the information travels through the C fibres to the dorsal root of the spinal cord, where it takes over until it reaches the brain. Specifically, the information travels until it is processed in the thalamus, somatosensory cortex, and hypothalamus where body temperature is controlled [2].

effects of high temperatures on the skin

Effects of heat on the skin

As temperatures rise, the body releases heat through sweating. In addition, it increases the heart rate and respiratory rate.

Loss of minerals with sweating

The higher the temperature, the greater the sweating. This process allows thermoregulation of the body through the sweat glands present in the skin [3].

With sweating, mineral salts are lost that can be replaced through the diet, mainly sodium and magnesium. Sodium plays an important role in the homeostasis of the body since it is responsible for water retention and therefore the balance of electrolytes.

In addition, sodium deposits found in the skin serve as reservoirs of this mineral in periods of scarcity. Specifically, sodium reserves located in the skin and on the endothelial surface function as buffers during periods of scarcity, representing an extrarenal mechanism that regulates sodium and body water [4].

Regarding magnesium, its deficiency induces an inflammatory response that results in the activation of leukocytes and macrophages, the release of inflammatory cytokines. In addition to an excessive production of free radicals [5]. Inflammation and oxidative stress influence the skin causing early aging in a process called inflammaging, which we already talked about in a previous post.

Transepidermal water loss

The hydration of the skin depends on several elements. In general, for the skin to be considered hydrated it must contain between 10 and 20% of transepidermal water. When these levels drop, dehydrated skin appears dull, rough, tight, and lacks flexibility. It can also produce a feeling of tightness and show dehydration scales and streaks [6].

Among the elements that maintain skin hydration we find:

  • Lipid barrier: Made up mainly of ceramides, it is found surrounding the corneocytes of the outermost layers of the skin, the stratum corneum.
  • Natural hydration factor: Made up mainly of free amino acids present in the intercellular spaces of the stratum corneum and whose main function is to absorb and retain water in this layer of the skin.
  • Stratum corneum enzymes: Such as SCCE or cathepsins D and E that are responsible for the cohesion between the corneocytes and the permeability of the stratum corneum.

Protect yourself from heat

Sun protection is essential when we expose our skin to avoid burns and the effects of solar radiation on the skin. But we must also ensure proper hydration that prevents transepidermal water loss.

For this, we can use different cosmetic preparations, generally aqueous phase emulsions that release water towards the stratum corneum. But it is also possible to use oil phase preparations that form an occlusive film that delays transepidermal water loss [6].

These preparations may contain:

  • Moisturizing ingredients that collect moisture from the environment and help preserve the degree of moisture caused by perspiration.
  • Occlusive ingredients that prevent transepidermal water loss by acting as a barrier.
  • Emollient ingredients that soften the skin tissue while promoting water retention in the stratum corneum.

In any case, the important thing to protect the skin from high temperatures is to keep it hydrated and protected from the effects of the sun and heat.

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References

  1. Caterina MJ, Schumacher MA, Tominaga M, Rosen TA, Levine JD, Julius D. The capsaicin receptor: a heat-activated ion channel in the pain pathway. 1997 Oct 23;389(6653):816-24.
  2. Zheng-Dong Zhao, Wen Z. Yang, Cuicui Gao, Xin Fu, Wen Zhang, Qian Zhou, Wanpeng Chen, Xinyan Ni, Jun-Kai Lin, Juan Yang, Xiao-Hong Xu, Wei L. Shen. Proceedings of the National Academy of Sciences Feb 2017, 114 (8) 2042-2047.
  3. Baker LB. Physiology of sweat gland function: The roles of sweating and sweat composition in human health. Temperature (Austin). 2019 Jul 17;6(3):211-259.
  4. Olde Engberink RHG, Selvarajah V, Vogt L. Clinical impact of tissue sodium storage. Pediatr Nephrol. 2020 Aug;35(8):1373-1380.
  5. Nielsen FH. Magnesium deficiency and increased inflammation: current perspectives. J Inflamm Res. 2018 Jan 18;11:25-34.
  6. Muñoz MJ. Hidratación cutánea. Estética y salud. Offarm. 2008 Dec. Vol 27. Num 11. 48-51.

Cover photo by Daoudi Aissa on Unsplash

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