7. Behavioural Thermoregulation: Understanding Our Fear of Heat

This chapter explores a topic that most of us rarely consider: how our mind regulates body temperature. While we all know we need oxygen and food to survive, staying at the right temperature is just as important. In fact, survival becomes a matter of minutes if we get too hot or too cold. Our bodies use an innovative system to stay balanced: we first try simple actions, such as seeking shade or bundling up, and only when that's not enough does our body kick in with sweating or shivering.

The chapter also examines how this instinct to regulate body temperature influences our social interactions. In cold countries, traditions like going to the sauna are not just about relaxation—they're part of a shared, cultural way of staying warm and connected. In hotter parts of the world, saunas didn't play a significant role in the past, but they've recently become more popular thanks to global wellness trends.

It also examines why some people fear heat or saunas, even if they've never had a bad experience. Our brains might be trying to protect us by predicting discomfort before it happens. Finally, the chapter explains how humans are uniquely designed to handle heat more effectively than many animals, thanks to traits such as walking upright and the ability to sweat.

Overall, this chapter demonstrates that maintaining our body temperature at the right level isn't just a background process—it influences our choices, traditions, and even friendships.

The Overlooked Significance of Thermoregulation

You've likely encountered a hierarchy of survival needs that ranks essential physiological requirements in order of importance. For instance, humans can survive without sunlight for years, food for a month or more, water or sleep for days, and oxygen for only a few minutes. But what about heat? Have you ever considered how maintaining optimal body temperature—thermoregulation—is one of our most immediate and critical physiological concerns, competing with the need to breathe? Probably not. Let's delve into this idea further.

We seldom consider our vital survival needs, particularly those the body manages instinctively without requiring conscious attention. For example, although oxygen is essential, we rarely think about the act of breathing. It occurs autonomously, a rhythm that hums quietly in the backdrop of our lives. It feels so natural and self-sustaining that it often goes unnoticed unless we consciously engage with it through meditation or specific breathing techniques. Breathing requires no adjustment of our social lives or behaviours, rendering it a silent yet ever-present necessity.

Food, on the other hand, demands our attention. Its lack of autonomy ensures it occupies a central place in our thoughts and actions. We think about it constantly, speak of it reverently, and elevate it to divine status through rituals and offerings. Food inspires books, competitions, and television programmes, driving cultural expression and survival strategies. In our consciousness, it holds a dominant position in the hierarchy of needs, rivalled only by reproduction—or, more specifically, making love. As Douglas J. Lisle and Alan Goldhamer note in The Pleasure Trap, this hierarchy remains intact unless one is male, in which case the order is reversed.

Where does maintaining optimal body temperature fit within this hierarchy?

Although often overlooked, warmth undoubtedly deserves to be ranked second in importance, right after oxygen, on any credible list of survival essentials. [1] Without adequate warmth or in extreme heat, survival time is alarmingly short, only slightly longer than without oxygen. Imagine standing naked on the summit of Mount Everest during a snowstorm. Or consider Professor Mike Tipton's finding that moderate exercise while wearing heat-retaining clothing can lead to fatal heat stress in just 25 minutes. Therefore, thermoregulation is a cornerstone of survival, yet its quiet significance often escapes our notice.

Unlike breathing, thermoregulation requires deliberate care throughout life. Parents or guardians assume this responsibility early on, ensuring a child's environment is neither too hot nor too cold. Later, it becomes a personal duty that silently shapes our daily lives.

Society's structure and routines often unconsciously prioritise thermal homeostasis. From the primitive need for shelter to the modern quest for a "warm home," thermoregulation has shaped human desires, behaviour, and relationships across millennia. Yet, we rarely contemplate its role with the same intentionality as food or reproduction—unless we are faced with extreme situations, such as homelessness, submersion in icy waters, or exposure to a wildfire. In such moments, the critical importance of thermoregulation becomes unmistakable.

The drive for warmth is fundamental, and its influence is woven into the fabric of human existence. Yet, its importance remains largely unacknowledged. It may be time to bring this essential priority into focus. Understanding and appreciating thermoregulation enhances our awareness and can significantly contribute to our health, well-being, and longevity. Shall we commence the exploration?

Thermoregulatory Hierarchy

By now, it is evident that regulating body temperature is vital for survival and development, as inadequate or poorly managed thermoregulation can lead to severe consequences. In response, nature has evolved highly efficient hierarchically organised systems to address bioenergetic constraints. Physiological mechanisms—such as sweating, shivering, and other autonomic responses—are inherently energy-intensive, making them unsustainable for prolonged use. Moreover, these autonomic responses have limited effectiveness in extreme environmental conditions. As a result, human thermoregulation prioritises behavioural adaptations as the first line of defence, engaging autonomic mechanisms only when necessary. [2]

Behavioural strategies include seeking more suitable environments, selecting appropriate clothing, adjusting body posture, and employing other reactive measures. When these strategies are insufficient, autonomic mechanisms are engaged. This hierarchical structure reflects an adaptation to energy efficiency, with behavioural responses serving as the primary, low-cost approach.

While this hierarchy is followed whenever possible, it usually operates unconsciously. For instance, individuals instinctively seek shade rather than relying solely on sweating or moving to warmer locations rather than enduring prolonged shivering.

In practice, thermoregulatory systems often function simultaneously. For example, when exposed to heat, individuals may sweat while simultaneously seeking shade. Autonomic systems typically act as supplemental tools to behavioural and social thermoregulation, as their effectiveness in extreme conditions is limited to short durations, such as tens of minutes in a sauna or icy water.

Overall, human thermoregulation is a complex, hierarchical system that combines autonomous and voluntary responses to maintain internal stability. This layered design provides both adaptability and efficiency. With that in mind, let's now explore the behavioural and social strategies involved.

Social Thermoregulation in the Light of Sauna

The concept of "social thermoregulation" is likely unfamiliar to most outside specialised fields. This is unsurprising, as it received limited attention even within professional circles for a considerable time. However, with the advancements in behavioural biology and biopsychology and the pursuit of more profound insights into the causes and consequences of behaviour, social and behavioural thermoregulation have gained increasing recognition and relevance. Some experts even argue that social thermoregulation plays a pivotal role in shaping social life—a thesis that finds compelling support in cultural practices, such as the sauna tradition in Northern European countries.

In these regions, where much of the year is characterised by cold weather, visiting a sauna is less a conscious decision and more an ingrained habit rooted in tradition. Traditions often have underlying purposes, though they may not always appear rational at first glance. In the case of saunas, however, the rationale is clear. In a predominantly cold climate, the prospect of a sauna can act as a potent motivator, releasing dopamine—the so-called "motivational hormone"—and fostering both physical and social warmth.

In contrast, the sauna has historically held little significance in regions with consistently warm climates. For example, it is hard to imagine that on the Canary Islands, famous for their eternal spring, or in the scorching heat of the Libyan desert, the thought of entering a sauna would evoke anything other than discomfort. However, because sauna use can help strengthen the body's thermoregulatory systems, it may still offer benefits even in hot climates. This perception is gradually evolving with globalisation and increased migration. In recent decades, saunas have become a standard feature in spa and wellness centres across the globe, including in warmer regions. While this trend is likely driven by modern health and relaxation values, it does not reflect a traditional need for social thermoregulation.

Still, the sauna tradition vividly illustrates how thermoregulation can influence human societies and the ways in which people interact with one another. Examples of such influences are evident across various cultural practices. This naturally raises the question: does thermoregulation also condition individual behaviour?

Behavioural Thermoregulation

Years ago, I encountered an acquaintance on my way to a sauna centre. It was a bright, sunny, and rather hot day. Since I had some spare time, we stopped at a nearby café for a drink. During our conversation, I mentioned my destination. At first, he frowned slightly, then, with a serious expression, asked if I wasn't afraid. Perplexed, I asked why, and he quickly clarified: "You know, the heat in a sauna can cook you like a frog in boiling water!"

Initially, I thought he was joking, but it soon became clear he was serious. I explained that the story of the boiling frog—a myth claiming that a frog will be boiled alive if the water's temperature increases gradually—was a fallacy often used by politicians with questionable motives. I reassured him that animals and humans possess advanced thermoregulatory systems capable of managing even the heat of a sauna, adding a touch of sarcasm, saying, "If, of course, we know what we are doing."

At the mention of the sauna, he seemed to grow uneasy, as if a latent fear had been triggered. Curious, I asked if he had any negative experiences with saunas or extreme heat. "You know," I said, "Whoever has been bitten by a snake is often afraid of even a twisted rope." To my surprise, he admitted he had never been to a sauna.

This left me wondering: Where does such fear originate if there's no prior experience? At the time, I was unaware of thermophobia—the irrational fear of heat—or the concept of behavioural thermoregulation. 

Experts in neuroscience suggest that, among its many roles, the brain acts as a predictive machine. [3] Anticipatory mechanisms, part of homeostatic control, often activate before an actual experience demands energy-intensive physiological responses. In this case, it's possible his brain formed an image of the sauna that triggered a strong stress response, leading to avoidance behaviour. This reaction might have served to conserve energy that would otherwise be required for cooling. While I cannot know this with certainty, the explanation seems logical.

He would likely justify his reaction as an exercise of free will. However, I'd argue that the brain's capacity to respond to logical arguments could lead him to reconsider. Perhaps after reading this book, he may associate saunas with health benefits and even positive experiences rather than the myth of the boiling frog.

Even such unconscious aversions to saunas can be classified as behavioural thermoregulation. This concept also encompasses many other behaviours, such as selecting appropriate clothing, choosing means of transport, or even deciding on the company we keep.

An interesting example of behavioural thermoregulation—though I did not recognise it as such at the time—occurred during my military service. In the dead of winter, with temperatures plummeting to around -20°C, we endured a two-week-long tactical exercise amidst a storm. The cold caused significant challenges, including the inability to start the diesel engines of military trucks and even tanks. Nights were especially gruelling.

We attempted to sleep in improvised tents constructed from a 2x2 meter military canvas, part of our personal equipment. Three soldiers would work together: one canvas served as a groundsheet, while two others were tied and hung between trees to form a makeshift tent. A thin blanket was our only cover, supplemented by any dry leaves we could scavenge.

To stay warm, we had to lie on our sides and huddle together in what we called the "spoon" position. The soldier in the middle—dubbed the "lucky one"—enjoyed the most warmth, and we took turns rotating through the middle spot every hour or two. Under normal circumstances, this arrangement would have been unthinkable. But as the saying goes, "Desperate times call for desperate measures."

To this day, I sometimes wonder if the warmth I feel when recalling my army friend Zoran (Pava)—my companion in those harsh conditions—is tied to the literal and figurative closeness we shared. Our friendship, forged in adversity, remains strong 30 years later, a testament to the enduring bond created by shared experiences of behavioural thermoregulation.

Excessive heat is equally concerning. Overheating poses even more significant challenges than inadequate heating. Our ancestors developed various methods to keep warm, including using caves and wearing furs. However, protecting ourselves from fire presents an entirely different challenge. Through the ages, we have cultivated a fear of fire. Sometimes, we even shape our culture around it. Hell is undeniably fiery hot, and a sauna is hot as hell; there is no doubt about that.

But there is good news. We are not alone in this battle. Humans have remarkable thermoregulatory capabilities that safeguard against overheating and efficiently dissipate heat, even during strenuous physical activity in warm environments. This vital ability has granted us significant selective advantages throughout human evolution.

I'm not talking about sweating—at least not yet. Other exchanges are going on that we rarely stop to consider.

As evolutionary biologist Professor Daniel Lieberman notes, the earliest hominins (species more closely related to humans than chimpanzees) likely diverged from the chimpanzee lineage due to selective pressures favouring bipedalism. [4]

Walking on two legs improved their ability to forage across varied landscapes. While bipedal locomotion made early hominins slower runners, it conferred an advantage in heat dissipation, enabling them to hunt during the hottest parts of the day. This adaptation provided safety from large predators that lacked such thermoregulatory efficiency.

Moreover, this superior heat-dissipation ability allowed early humans to engage in persistent hunting. They could pursue faster, four-legged prey, such as antelopes, whose heat regulation was limited to panting and tongue-based cooling. By exploiting their endurance and heat resilience, human hunters could drive these animals to exhaustion and heatstroke, ultimately securing them as a food source.

The thermoregulatory advantages of an upright posture are evident. An upright stance reduces the surface area exposed to direct solar radiation, minimising heat absorption. Additionally, walking upright increases skin exposure to airflow, which enhances evaporation and accelerates heat loss. Furthermore, bipedal locomotion is more energy-efficient, requiring a lower metabolic rate and consequently generating less heat. This efficiency is especially critical given that muscle contraction converts only about 20% of energy into movement, with the remaining 80% released as heat that must be dissipated, particularly in hot environments. All things considered, the push for better thermoregulation is a significant reason we ended up on two feet and, in many ways, changed our behaviour. It's not the only factor, but it's an important one. Having our heads held higher gave us a better view of our surroundings and helped us spot fires sooner.

This raises another question: what enables humans to maintain optimal body temperature and effectively dissipate heat while performing demanding physical tasks in high temperatures?

Professor Michael N. Sawka [5] highlights two unique thermoregulatory features in humans that account for this capability:

Dynamic Core Temperature Regulation: Humans naturally maintain a balanced core temperature, which encompasses vital organs and the brain, even during physical activity. This happens through metabolic adjustments that work independently of the surrounding environment. Simply put, our metabolism constantly adapts to help regulate body heat as needed.

Efficient Heat Dissipation: Humans are adept at dissipating excess heat, primarily through sweating and increasing blood flow to the skin. However, this ability also comes with challenges, such as added strain on the heart as the body works to regulate its temperature. Luckily, the skin and some internal organs have built-in mechanisms to help manage this, which we'll explore further in the chapter on how sauna use affects the heart.

In summary, social and behavioural thermoregulation acts as the first line of defence against extreme temperatures. These factors also play a significant role in shaping our responses to the sauna. If you're not immediately drawn to the idea of a sauna, it's a sign that your behavioural thermoregulation is functioning correctly. After all, the prospect of enduring 100 degrees Celsius can be understandably daunting.

That said, I encourage you to continue reading, as what may initially feel like resistance could ultimately transform into a profoundly beneficial and enjoyable experience. But more on that later. First, let's explore an intriguing question: why is the sauna so helpful, even though it places considerable stress on the body?