There are many ways to describe my mood as I left my meeting with Professor Chambers, but ‘happy’ wasn’t one of them. It was a long and miserable walk home as I worried about what to do next.

However, as I arrived at my street, something odd happened; I caught sight of my house, and I started to feel better. No intense euphoria or giddy high, but a definite sense of positivity and relief, probably not something I’d usually notice but in my current downcast state it was a stark change. When I actually went into my house my mood improved further. My thinking changed from ‘What am I supposed to do now?’ to ‘What AM I going to do now? What’ll I look at next?’ The former suggests despondency; the latter action, motivation, engagement. Arriving home had improved my mood. A lot of people report similar experiences, the sheer relief and pleasure in getting home after an arduous journey or long work day. It’s a very common feeling. You could say our homes, in various ways, make us happy.

Is that right? Is it just the sense of an otherwise unpleasant task or series of events coming to an end when we arrive at our own doorstep, or is there something about our home that triggers positive feelings in our brain? What is going on in there?

Neuroscientifically, the idea of our homes making us happy doesn’t make much sense. Neurologically, we quickly adapt to familiar things. Neurons stop responding to signals and stimuli that occur repeatedly and predictably.1 Think about when you walk into a kitchen where someone is cooking something pungent, like fish. It stinks! But after a few minutes, you stop noticing. Then someone else comes in, moans about the smell, and you wonder what they’re complaining about. That’s habituation. When you get dressed you quickly stop ‘sensing’ the feeling of your clothes. That’s habituation too. Studies show that people can even get used to electric shocks,2 as long as they’re predictable, and relatively mild. Habituation is a powerful process which means the brain immediately focuses on any sudden changes in our situation, but if it hangs around and doesn’t do anything important, the brain essentially loses interest.

We spend maybe half our waking (and nearly all of our sleeping) lives in our homes, so you’d think they’d be the last thing our brain responds to. Why, then, does the home provoke a response in our brains that results in us being happy?

As with ‘happiness chemicals’, this argument seriously oversimplifies how the brain works. Our brains and nervous systems do stop responding to things, as long as they are not biologically relevant. This is key; it means we stop responding to things that have no biological consequence.

We need food. We eat it several times a day. But do you ever get ‘bored’ of food? You can tire of types of food; eat nothing but pasta for a week and you’ll quickly get fed up with it. But the act of eating, consuming food, that never gets dull.* The most mundane meal can, when hungry, provide feelings of satisfaction, contentment, pleasure, happiness? Even a glass of water seems like divine ambrosia from God’s own keg if you’re hot or thirsty, because it’s biologically relevant. Our brains recognise it as something we need in order to stay alive, so rewards us with pleasurable feelings when we obtain it.3

It’s not just nice things. People may quickly get used to the temperature of water that they’re immersed in, but not if it’s literally scalding, because this causes severe pain, something our brains rarely, if ever, fully adapt to. The initial intensity may subside, but pain suggests damage has occurred, or is occurring, to the body. This is very biologically relevant, so mustn’t be ignored. Pain even has its own dedicated neurotransmitters, receptors and neurons,4 all dedicated to ‘nociception’, the perception of pain. It’s essential, if unpleasant.

Our brains ‘overrule’ habituation when it comes to important things. And if they’re positive, beneficial things, this activates the reward pathway, meaning we experience some form of pleasure whenever we encounter them. So, there are some things we remain keen on and responsive to, regardless of familiarity.

What’s this got to do with home? Are our homes ‘biologically significant’? Quite possibly. Consider all the essential things that happen within your home: nourishment, sleeping facilities, warmth, even plumbing (expelling bodily waste is another vital function).

Pavlov’s famous dogs learned that an innocuous sound meant that food was forthcoming and responded enthusiastically as a result,†5 establishing the fundamentals of associative learning, where mental connections are made between separate occurrences. It takes the formidable human brain no time to learn that our home is where all our biological essentials can be found, so we form a positive association with it.

But this is a learned thing. Our home isn’t doing anything biologically relevant, it is just where biologically relevant things happen. Is there anything to suggest that our brains respond to our homes directly? To answer this, look at the fact that homes are naturally occurring.

Homes aren’t something humans invented for somewhere convenient to keep our shoes and iPads. They occur everywhere in the natural world, in many different forms: birds’ nests, anthills, termite mounds, rabbit warrens, bears’ dens, and many more. Countless species have homes; we humans are just the first to come up with doorbells.

If something is common in a wide range of species, it strongly suggests a biological need is being met. Evidence points to a sense of safety. Biologically relevant things typically keep us alive, help ensure our survival. But, in nature, it’s not just lack of food that kills you; there are countless dangers and threats out there, most obviously predators, but environmental hazards too. Abundant food is useless if you slip into a shadowy ravine and break your neck.

As a result, even the most basic mammal has evolved a complex and sensitive threat detection mechanism. In humans, regions like the amygdala, subgenual anterior cingulate cortex, superior temporal gyrus, fusiform gyrus and more6 form part of an intricate network that rapidly processes information from the senses, evaluates it for anything that looks like a threat, and triggers the appropriate reaction (e.g. the fight-or-flight response). This threat detection system is incredibly useful when exploring new, unfamiliar locations, looking for resources or mates but not knowing if hungry carnivores are lurking in the shadows.

But it’s not something we just switch on when we think it might be useful, like taking an umbrella when it might rain; it’s ever-present, ready to spring into action at the faintest whiff of danger. Some evidence suggests it can even be triggered by a simple shape. A 2009 study by Christine Larson and colleagues7 showed these threat-detecting areas became more active when presented with basic 2D shapes composed of downward-pointing ‘V’s. Essentially, pointy triangles set off the threat-detection system. Not substantially so, or we’d be quaking in fear at the sight of the alphabet, or kites. But still. It even makes a certain sense; many natural dangers, like a wolf’s face, fangs, talons, spikes, etc. all have general ‘V’ shapes. Our evolving brains spotted this, and became wary of it.

Our brain’s threat-detection systems are sensitive and persistent, but constant fear and paranoia is very debilitating, as anyone with chronic anxiety will tell you.8 It’s an extremely stressful way to live, impacting negatively on the health of your body and brain. People who suffer from anxiety often feel unable to leave home. This makes sense; familiar places are less dangerous – you’ve been there often and haven’t died, so your threat-detection system isn’t dialled up to maximum, like a sniper on amphetamines. Instead it’s turned way down, like a night watchman at a village shoe shop; still vigilant, but not really anticipating having to do anything. It’s very helpful to have access to a reliably safe and familiar place, to stop the effects of constant fear and stress. And voilà, a clear biological benefit of having a home.

What is interesting is that when we are at home, we can more easily focus on anything out of the ordinary. If you’re in an unfamiliar restaurant and hear a glass smash, it’s distracting for a moment, but then technically everything is, because everything’s unfamiliar, so you pay it only cursory attention. You’re in your own home and hear a glass smash? That’s unusual, suddenly you’re primed for danger because you know it’s a hazard (doubly so if you’re home alone). Some studies even suggest we can detect and recognise threatening stimuli faster in a familiar environment than in an unfamiliar one.9 It makes sense; there’s less to distract us, our brain is used to ‘ignoring’ the environment around us, so anything that differs from that gets our attention much faster. A tiger in the jungle can be hard to spot; a tiger on a cricket pitch is not.

Providing a reliable environment where we can be stress-free is one way that our homes can make us happy. This isn’t to say that our home is automatically stress-free. It can be a source of great anxiety, but more often...