The skin functions as a protective barrier, allowing us to maintain homeostasis of the body. But, in addition, the skin functions as the first receptor of the outside world: in the epidermis and dermis we can find sensory receptors that inform us about the temperature of the environment or the touch of objects. 

Sensory receptors are specialized neurons and cells that have ion channels that activate them when they perceive a tactile, thermal and/or painful stimulus. Ion channels are formed by a set of specific proteins present in the cell membrane and that, when activated, allow ions to pass through activating the cells and/or neurons. 

In cosmetics, these receptors have been widely studied since they participate in the sensoriality of the skin and in maintaining its correct homeostasis. 

In this post, we are going to talk about some of the most interesting receptors for the cosmetic sector: 

Touch receptors 

The skin has various receptors for the sensation of touch, both in the dermis and epidermis. They differ, fundamentally, in the threshold at which they can be activated. Thus we find: 

To low threshold receptors. As are the corpuscles of Merkel, Meissner, Pacini and Ruffini. All of them are located in the dermis, in the most superficial layers, and are responsible for reporting stimuli on soft-touch skin (1). 

On the other hand, high threshold receptors are the so-called free nerve endings that are responsible for coarse and even painful touch stimuli. 

In addition to their activation threshold, these receptors differ in their ability to adapt. Thus, the corpuscles of Merkel and Ruffini are from the group of those called slow adaptation, while those of Meissner and Pacini are fast adaptation1. 

What does it mean for a receptor to adapt quickly? When a rapidly adapting receptor is activated, it will react to the beginning and end of the stimulus, that is, when there is a change since they have quickly adapted to the type of stimulus. 

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How do touch receptors work? 

Touch receptors, or mechanoreceptors, are activated by tactile stimuli thanks to a series of proteins that they have in their membrane. The most important family of mechanical receptors is known as PIEZO and in particular, a member of this family called PIEZO2. 

PIEZO2 is an ion channel that, when activated by mechanical stimuli of a certain intensity, opens, activating, among others, the Merkel cells present in the skin. This activation is subsequently transferred to a sensory neuron that carries the information to the somatosensory cortex of the brain via the spinal cord (2). 

Temperature receptors 

The regulation of body temperature is, to a large extent, thanks to the action of other types of receptors in the skin. To detect high temperatures, we have a series of ion channels in our dermis that are activated when a certain temperature is reached. 

Temperature detection is carried out through the free neuronal endings present in the skin and which express a series of ion channels in its membrane. For heat detection we have the TRPV1 channel and it is activated with temperatures above 42ºC (3). 

On the other hand, to detect low temperatures, humans have two receptors from the same family in our skin: TRPM8 and TRPA1. The first is considered the recipient of moderate cold, since it is activated at temperatures below 26ºC (4). While TRPA1 does so at temperatures below 10ºC (5). 

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All of these temperature receptors belong to the TRP family of channels. These receptors are calcium channels that, when activated, allow calcium and other ions to pass through, activating the free nerve endings and informing the brain of the external temperature using the same route that the sensation of itch takes to the somatosensory cortex. 

There, tactile and temperature information is processed differently to generate a response according to the stimulus received. 

If you want to learn more about the types of skin receptors, visit our YouTube channel. 

When something goes wrong: The feeling of itching and stinging 

So far we have seen what the skin receptors are and how do they work when external stimuli are harmless. But what happens when something goes wrong? 

Certain dermatological diseases such as atopic dermatitis, rosacea or psoriasis are accompanied by a constant itching sensation. This sensation is very annoying and affects the quality of life of people who suffer from these diseases. 

The molecules that are involved in the onset of the itchy skin sensation are histamine, substance P, serotonin, b-natriuretic polypeptide, periostin, endothelin-1, and neuropeptide Y (6). All of them act by recruiting cells of the immune and neuronal system. 

The activation of sensory neurons through these molecules occurs through the TRPV1 and TRPA1 receptors, these channels that, as we have seen, are also activated by changes in temperature. 

Both channels are usually expressed together in the sensory neurons responsible for the sensations of itch and pain called nociceptive neurons. Therefore, the activation of these channels leads to greater activity of these neurons, causing an exacerbated sensation of itching and/or pain. 

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How to calm itchy skin 

In situations where our skin is tight due to a lack of moisture or in sensitive skin, this itching can be very annoying. For this reason, AntalGenics has developed Calmapsin®, an innovative neurocosmetic ingredient that helps maintain the quality of the skin by acting to reduce the sensation of itching thanks to its calming effect on the skin’s sensory neurons. In addition, Calmapsin® improves hydration, by preventing the reduction in the expression of genes involved in the skin’s barrier function, and protects it thanks to its antioxidant action. 

Discover more about our innovative neurocosmetic ingredient for itchy skin through the following video. 

References

  1. Abraira, V. E., & Ginty, D. D. (2013). The sensory neurons of touch. Neuron, 79(4), 618–639. https://doi.org/10.1016/j.neuron.2013.07.051 
  2. Anderson, E. O., Schneider, E. R., & Bagriantsev, S. N. (2017). Piezo2 in Cutaneous and Proprioceptive Mechanotransduction in Vertebrates. Current topics in membranes, 79, 197–217. https://doi.org/10.1016/bs.ctm.2016.11.002 
  3. Caterina, M. J., Leffler, A., Malmberg, A. B., Martin, W. J., Trafton, J., Petersen-Zeitz, K. R., Koltzenburg, M., Basbaum, A. I., & Julius, D. (2000). Impaired nociception and pain sensation in mice lacking the capsaicin receptor. Science (New York, N.Y.), 288(5464), 306–313. https://doi.org/10.1126/science.288.5464.306 
  4. McKemy, D. D., Neuhausser, W. M., & Julius, D. (2002). Identification of a cold receptor reveals a general role for TRP channels in thermosensation. Nature, 416(6876), 52–58. https://doi.org/10.1038/nature719 
  5. Story, G. M., Peier, A. M., Reeve, A. J., Eid, S. R., Mosbacher, J., Hricik, T. R., Earley, T. J., Hergarden, A. C., Andersson, D. A., Hwang, S. W., McIntyre, P., Jegla, T., Bevan, S., & Patapoutian, A. (2003). ANKTM1, a TRP-like channel expressed in nociceptive neurons, is activated by cold temperatures. Cell, 112(6), 819–829. https://doi.org/10.1016/s0092-8674(03)00158-2 
  6. Navarro-Triviño F. J. (2023). Pruritus in Dermatology: Part 1 – General Concepts and Pruritogens. Prurito en dermatología. Generalidades y pruritógenos. Parte 1. Actas dermo-sifiliograficas, 114(6), 512–522. https://doi.org/10.1016/j.ad.2023.03.003 

    Cover image by Ximena Mora from Pexels

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