International Hug Day丨Why does a loving hug stimulate our “tactile pleasure”?

Hugging, this simple yet powerful physical gesture, is a way of expressing love that we often overlook in our daily lives. In order to encourage everyone to hug their family and friends more often, American Kevin Zaborney initiated National Hugging Day in 1986, which is held on January 21 every year.

Why is the simple act of hugging such a wonderful experience? Where does its magic come from?

"Pleasant touch" makes us fall in love with hugs

For humans, the tactile system is not only the most widely distributed sensory system, but also the earliest sense that allows humans to feel cared for, loved, and safe. While the sense of touch creates a unique sensory experience for humans, it also makes humans fall in love with hugs.

Copyright images in the gallery. Reprinting and using them may lead to copyright disputes.

In 2022, a study published in the journal Science found that if you stroke the back of a mouse with a brush, the mouse's heart rate will drop, its tolerance to pain will increase, and the level of stress hormones in its plasma will also decrease . The researchers speculate that this is because animals have a special sensory system that can be activated by positive social touches such as gentle stroking and hugging. They define it as: pleasant touch . They found that when mice enjoy "fur brushing", the PROKR2 neurons in their spinal cords are activated. When scientists destroy this neuron, the mice become indifferent, unwilling to stick with their companions, and do not like to be brushed.

A year later, another study published in the journal Cell once again proved the existence of "pleasant touch" and found special neurons used to feel this touch - Mrgprb4 neurons. This is a type of neuron distributed on the skin. When the skin feels hugs and caresses, this group of neurons will send signals to the brain, which will be transmitted step by step to the brain areas related to rewards and pleasant experiences, and promote the brain to release "happy hormones" - dopamine . Under this mechanism, the brain will regard a hug as a reward signal that can bring happiness.

When we hug, our bodies...

The simple action of hugging awakens not only the "pleasant sense of touch", but also a series of physiological changes.

Some studies on married couples have found that hugging increases their oxytocin levels . Oxytocin, also known as the "cuddle hormone," is a hormone that increases intimacy and trust and reduces anxiety. For this reason, hugging can make people feel safe, and frequent hugging can deepen the relationship between lovers.

Oxytocin also has an important function - activating the sympathetic nervous system, switching the body's working mode from "movement" to "stillness", from tension to relaxation. Therefore, a large number of studies have reported that hugging can reduce heart rate, lower blood pressure, and calm the mood. A warm hug before going to bed can bring higher quality sleep .

Hugging can also make the brain secrete endorphins and serotonin . Endorphins are hormones secreted by the pituitary gland and are natural analgesics in the body. Therefore, hugging when you feel uncomfortable can have a physiological analgesic effect. Serotonin is the "happiness hormone" in our body, which can continuously send positive emotional signals to the body, and can bring us a positive attitude and a feeling of happiness. Therefore, when you are in a bad mood, a big hug can really lift your spirits.

Copyright images in the gallery. Reprinting and using them may lead to copyright disputes.

Hugging can also expel negative energy from the body. When you hug tightly, the level of cortisol, a "stress hormone", in your body will decrease, and your ability to resist stress will increase . However, this study showed differences between men and women. The men who participated in the experiment did not show a significant decrease. The researchers said that this may be due to social factors. Hugging is an embarrassing behavior for many men.

Can hugging often improve immunity?

Modern people live a fast-paced life and are often in a high-pressure environment. They are not only prone to negative emotions such as anxiety and depression, but also have a lower resistance. In this regard, the research team of Carnegie Mellon University proposed a very simple method - hug others more often to improve resistance !

Copyright images in the gallery. Reprinting and using them may lead to copyright disputes.

The team surveyed 404 healthy adults, asked them about recent interpersonal conflicts to assess their recent social stress, and recorded the frequency of their hugs to understand their social support, and then exposed them to the influenza virus. The results showed that among the infected volunteers, those who had more social support (more frequent hugs) had milder symptoms. The researchers explained that the social stress caused by interpersonal conflicts can lead to a decrease in the immune system's ability to fight disease. Being hugged by a trusted person is a strong social support that helps relieve stress and prevents stress from weakening the immune system.

If you are under pressure, you might as well try this method and spend some time with the people you love!

References

[1]Elias, LJ, et al., Touch neurons underlying dopaminergic pleasurable touch and sexual receptivity. Cell, 2023. 186(3): p. 577-590 e16.

[2]Liu, B., et al., Molecular and neural basis of pleasant touch sensation. Science, 2022. 376(6592): p. 483-491.

[3]Holt-Lunstad J, Birmingham WA, Light KC. Influence of a "warm touch" support enhancement intervention among married couples on ambulatory blood pressure, oxytocin, alpha amylase, and cortisol. Psychosom Med. 2008 Nov;70(9):976-85. doi: 10.1097/PSY.0b013e318187aef7. Epub 2008 Oct 8. PMID: 18842740.

[4]Grewen KM, Anderson BJ, Girdler SS, Light KC. Warm partner contact is related to lower cardiovascular reactivity. Behav Med. 2003 Fall;29(3):123-30. doi: 10.1080/08964280309596065. PMID: 15206831.

[5]Cohen S, Janicki-Deverts D, Turner RB, Doyle WJ. Does hugging provide stress-buffering social support? A study of susceptibility to upper respiratory infection and illness. Psychol Sci. 2015 Feb;26(2):135-47. doi: 10.1177/0956797614559284. Epub 2014 Dec 19. PMID: 25526910; PMCID: PMC4323947.

[6]Ditzen B, Neumann ID, Bodenmann G, von Dawans B, Turner RA, Ehlert U, Heinrichs M. Effects of different kinds of couple interaction on cortisol and heart rate responses to stress in women. Psychoneuroendocrinology. 2007 Jun;32(5):565-74. doi: 10.1016/j.psyneuen.2007.03.011. Epub 2007 May 11. PMID: 17499441.

[7]Dreisoerner A, Junker NM, Schlotz W, Heimrich J, Bloemeke S, Ditzen B, van Dick R. Self-soothing touch and being hugged reduce cortisol responses to stress: A randomized controlled trial on stress, physical touch, and social identity. Compr Psychoneuroendocrinol. 2021 Oct 8;8:100091. doi: 10.1016/j.cpnec.2021.100091. PMID: 35757667; PMCID: PMC9216399.

[8]Berretz, G., et al., Romantic partner embraces reduce cortisol release after acute stress induction in women but not in men. PLoS One, 2022. 17(5): p. e0266887.

Planning and production

This article is a work of Science Popularization China-Starry Sky Project

Produced by: Science Popularization Department of China Association for Science and Technology

Producer｜China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.

Author: Hardy, PhD in Neurobiology, Zhejiang University

Reviewer: Li Jingjing Professor and Chief Physician, Department of Neurology, Beijing Tiantan Hospital

Planning丨Lin Lin

Editor: He Tong