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There has been a lot of talk recently about ‘skin hunger’, the feeling of a craving alike to the sensation of hunger, but not for food, but for human touch. This is craving is thought to be caused by the isolation from others that we are experiencing as part of the social distancing and lockdown measures to control the spread of COVID19.
What is going on here? There is plenty of evidence that touch from loved ones can improve mental and physical well-being (see here, here and here). But can we really speak of a skin hunger? A longing to touch others? I am a psychologist, so I am not well versed in biology or physiology. But I have worked on pain processes, which share some interesting similarities with the processing of touch.
Touch is one of our first sensations when we come into this world. Touch is fundamental for communicating with others – when we feel sad, a hug can often say more than a thousand words. A hard grasp by the shoulder in the dark is also more menacing that my description can convey just now. However, touch is not an easy thing to understand or take apart.
In order to start to understand how important touch is, we need to first realize how central it is for us humans. Just think of your skin – it covers the whole exterior of your body. The adult person is said to have about 18,000 square centimeters of skin – this is nearly 2 square meters of skin that account for up to 18% of your body weight. All of this surface is full of nerve cells. There are thermoreceptors that respond to warmth or cold; there are nociceptors that respond to different types of pain, skin irritation and itch, and there are mechanoreceptors that react when our skin is touched or stretched (which can also happen when we move our muscles). These receptors are unevenly distributed on our skin. There are some receptors that are only found on hairy skin (e.g., your forearm) and other types of receptors that are primarily found on skin that has no hair cells (such as your palm). There are some recently discovered nerve fibres that have created quite a bit of research and excitement because they seem to be crucially involved if we want to understand the emotional meaning of touching. This special class of mechanoreceptors called C-tactile (CT) afferents is only found in hairy skin. These nerve cells are unmyelinated axons (they don’t have a fancy coating around them) and send signals very slowly to the brain. These nerve fibres differ from the others that are very frequent and fast, the A fibres which have that special type of coating and can send highly specific location and type of object (e.g., was it sharp, was it deep) information very fast to the brain. Think of a needle prick – this will activate the A fibres. The CT fibres only get activated if there is some slow motion of our skin and this information then travels relatively slowly to the brain.
Our brain now will receive a million of signals from different fibres – where is there some connection with something, how warm or cold is it, is it itchy, how fast is the object moving, how strong is the indention on my skin, etc. All of this information needs to be integrated with other information from the sense, like our eyes, ears and nose. This information will be checked against our memory – where am I right now – have I been here before – what has happened at similar points in time. This information integration is happening really fast. Importantly, our brain makes predictions based on previous experiences to help us make fast decisions about whether it is a dangerous or pleasant situation. This is what is called predictive information processing. There are some estimates that about 80% of our experiences are driven by internal processes – basically by what we have experienced before and this is mapped onto the incoming information from our eyes, ears and of course, our skin. Only if there is some really strange misfit between what we are expecting and what is coming in from our senses will be there an adjustment and actually will experience the world as our sensations are telling us. The rest of the time, we are living in a fancy imagination of our past projected on the here and now. This sounds pretty crazy – doesn’t it, but this is best understanding that we currently have about how our brain is actually working and how it is able to make sense of all this information that is bombarding all our senses (and those nearly 2 square meters of skin of yours) all the time and without a break.
But what is happening with all that talk about hugging and oxytocin and stress reduction? If the incoming information is consistent with a pleasant prediction (e.g., you are with your partner, watching a sunset at the beach and the atmosphere ‘expects’ that your partner will put his or her arm around you), then there will be all sorts of chemical reactions – oxytocin will be released, increasing bonding responses; serotonin will be released decreasing stress. There is a firework of chemicals going on that make us feel relaxed and happy. On the other hand, if you are sitting on the beach alone, it is getting dark and you are not sure where you are, a sudden touch on your back would have completely the opposite reaction – your adrenalin would go up, cortisol would be released and your blood pressure would shoot up to get you ready for fight or flight. A classic stress reaction. Or thing of sexual foreplay – now touch will be electrifying, your blood pressure will also shoot up, adrenalin levels will increase and dopamine will be released in anticipation of all those pleasures that you have associated with having sex with your partner before. Hence, it is the context that is really important for helping our brain interpret touch.
Hence – our sense of touching like many other sensations is largely driven by our previous experiences, by what we are expecting in a given situation, by what we have learned to expect. It is at this point that cultural differences and cultural expectations come in. In some cultures and in some environments (think of a bar vs church) we are more likely to become touchy, whereas in others touch is much more restricted.
Now let’s come back to the idea of skin hunger. What is likely to happen in the current environment of social distancing is that we suddenly do not have the chance to experience these inputs that we are expecting in everyday situations. Our brain has learned that interactions come with touch, hand shakes, a kiss, a hug. Our interactions with friends and colleagues over the phone or social media now are missing one piece of input that is normally part of it. Hence, this may feel unbalanced or like something is missing. It is not like hunger, but it can still feel quite real because we have been so used to it.
In many ways it would be similar if all of a sudden we would not be able to hear or see, we would have a craving for stimulation of those senses that are deprived now. However, it is important to remember that it is the context that is as important. We might be longing for the feeling of a friend’s hug or our lover’s embrace, but we would still be scared to hug a menacing stranger that just broke into your apartment. Context matters. Skin hunger is a nice word to mean that we are longing to have all those sensations back that we have grown up with and that our brain is accustomed to when talking to those people that we care about. It is not so much a hunger or has little to do with skin, but more a missing communication input from interactions with those who are close to us.
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