Chillies are one of our most popular foods. Why do we always want the things that hurt us?

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The human fondness for chillies is an absurd thing.

Chillies are specifically designed, by the chilli plant, to be toxic to mammals, including, of course, humans.

The mammalian digestive systems destroys chilli seeds. This makes it a dead end as far as the chilli plants are concerned.

What chilli plants want is for birds, whose digestive system is kinder, to eat their chillies and disperse the seeds far and wide propagating the next generation of chilli plants. So chilli plants have made the chilli toxic to mammals and harmless to birds.

Birds can eat chillies with zero side effects and all mammals avoid chillies like the plague. All mammals, that is, except one absurd, bloody-minded species.

Yes I’m talking about us. Humans did not take the hint. Instead we made the toxic fruit of the chilli plant the foundation of some of out most popular cuisines.

In a giant ‘screw you’ from humans to chilli plants, chillies are now one of the most consumed food stuffs on the planet. You have to have some sympathy for the chilli plant, there’s no accounting for crazy.

OK, There’s one other crazy species

There is one small mammalian species that lives in the forests of South and Southeast Asia called the Tree Shrew that can and does eat chillies. This was only discovered in 2018 (you can read the paper here) but Tree Shrews have a genetic mutation in the TRPV1 receptor that makes them much less susceptible to capsaicin. So this species is more like birds in that they are not that bothered by chillies. The point that humans are definitely bothered by chillies but continue to eat them stands.

They Came From the New World

Humans of the New World had a long history with chillies but it wasn’t until the Columbian exchange, beginning at the end of the 15th century, that the rest of the world became aware of chillies.

It didn’t take long for chillies to establish themselves though. Both tomatoes and potatoes, the other famous new world imports, were at first treated with suspicion and often not widely accepted for decades or even centuries. Chillies, however, spread like wild-fire.

When chillies arrived in the old world from South America instead of people recoiling in horror from these devil fruits, it took about five minutes for them to become an integral part of old world cuisines.

Can you imagine Indian, Sri Lankan, Spanish, Chinese, Thai or Korean food without chillies? So quickly and so thoroughly were chillies incorporated into our Old World cuisines that it seems like we never didn’t have chillies.

Life Before Chillies

There was some precedent for chillies in the Old World.

Before the arrival of chillies, pepper was used to add spice to food and, as we’ll find out, pepper spice is similar to chilli spice.

Pepper was a big business in the 16th century so there was clearly a taste for spice already in the Old World. Chillies, being much easier to grow, were probably seen as a cheaper, easier pepper.

The difference is that chillies are very much more potent than pepper. But this potency in no way deterred their rapid incorporation into old world cuisines.

Our ancestors clearly saw that chillies were pepper on steroids and considered that a feature not a bug.

What Is Capsaicin, Where Is It Located and How Does it Hurt Us?

The magic ingredient that give chillies their potency is capsaicin.

You’ve probably heard of capsaicin before and that’s because it is famously responsible for almost all the noxious effects we associate with chillies.

Capsaicin is a small, colorless, hydrophobic and highly pungent molecule that is synthesised in the spongy membrane that supports the seeds inside the chilli.

Contrary to popular belief, capsaicin is not found in the seeds but is mostly found where it is made, in this spongy membrane (confusingly called the placenta).

How Capsaicin Triggers Pain: The TRPV1 Heat Receptor

Capsaicin causes it’s effects by binding to cell surface proteins that are a part of the bodies nociception system (a fancy way of saying ‘pain sensing’).

This system senses pain and alerts our brain when something bad is happening to our bodies.

In particular capsaicin binds to a protein heat receptor called TRPV1 and by doing so it essentially dupes our body into thinking that we are burning, that we are experiencing noxious levels of heat.

Usually capsaicin meets TRPV1 in the mouth after we eat spicy food, though anyone who has accidentally rubbed their eyes after handling chillies has learnt that TRPV1 receptors are lurking all over our body.

Cell Surface Receptors

To understand how capsaicin works it’s magic we need to get a handle on how cells sense and respond to their environment and the role that a receptor like TRPV1 plays in that process.

All cells are bristling with surface proteins stuck in their outer membrane. Cells have surface proteins that are tailored to the function that cell performs in the body.

Many of these proteins can interact with the cells environment by sensing molecules outside the cell or responding to other environmental conditions. These proteins will initiate some type of cellular response when activated.

Cell surface proteins like these are grouped into a broad group called receptors. There are many different types of receptors but the important ones for capsaicin bioactivity are called ion channel receptors.

The Cellular Mechanism: Dupping the Brain with Heat Signals

An ion channel is a protein receptor that, when activated, will open and allow charged molecules, or ions, to enter the cell. Ion channels make nerve impulses possible by enabling the propagation of an electrical potential along neurons to the brain (and vice versa).

TRPV1 is an ion channel receptor that sits on the surface of a sensory neuron. If it is experiencing a temperature greater than about 40$\degree$C it will open and the influx of charged ions will enter the cell and kick off a signal to your brain.

This initial signal in turn triggers a bunch of responses designed to protect our body from excessive heat (sweating and blushing for example).

When capsaicin binds to TRPV1 it causes the exact same response as if the receptor was detecting heat and the body responds appropriately.

This makes intuitive sense, when we eat chillies it’s like we are experiencing heat; our mouths burn, we flush, we sweat and we experience all the ‘symptoms’ of heat.

All this happens because capsaicin has duped our body into thinking it is experiencing noxious heat.

Comparing Pungent Compounds in Common Spices

There’s a lot of science behind the binding of drugs to cell receptors and some of this science can help us understand how capsaicin works.

Capsaicin, for example, has a high affinity for TRPV1 (it binds tightly to the ion channel) and a high efficacy (it produces a large response for a given dosage).

This explains why chillies have a strong effect that lasts for a comparatively long time. Once it’s bound, it’s hard to get capsaicin out of the receptor.

Black pepper has a similar activity to chillies and this is because it contains a molecule, called piperine, that also binds TRPV1. But piperine has a different structure and a lower efficacy. That is, it elicits a much less potent TRPV1 response.

Binding and response kinetics also explain the responses we have to other molecules from the same family we find in our food.

Molecule	Found In	Target Receptor	Relative Burn Intensity	Key Characteristics
Capsaicin	Chilli peppers	TRPV1	Very High	High affinity & efficacy; hydrophobic, long-lasting bind
Piperine	Black pepper	TRPV1	Moderate	Structural cousin to capsaicin; milder heat response
Gingerol	Fresh ginger	TRPV1	Mild to Moderate	Warm sensation; converts to zingerone when cooked
Hydroxy-α-sanshool	Sichuan pepper	TRPV1 / KCNK	Mild + Tingling	Triggers both heat pain and tactile vibration (numbness)
Vanillin	Vanilla	TRPV1	Negligible	Weak agonist; binds without triggering noticeable pain

For example gingerol, from ginger, hydroxy-alpha-sanshool, from Sichuan peppers, and vanillin, from vanilla, all bind to TRPV1 in ways that elicit greater or lesser responses.

Vanillin, for example, is a very weak agonist of TRPV1 (an agonist activates a cell receptor and an antagonist deactivates it) . Which is why we don’t associate vanilla ice cream with chilli burn.

Why Milk Beats Water and Acidic Drinks If You Want Some Relief

Binding kinetics also informs the constant debate about the best way to alleviate chilli burn.

If you get on the internet there are a lot of opinions but it has been studied, to some extent, and current scientific opinion backs up the idea that drinking milk is the best way to get rid of chilli burn.

Traditionally it was thought that because capsaicin is hydrophobic, something with a higher fat content would enhance it’s solubility (for an in depth look at why this is so see the emulsions post).

But more recent work suggests casein, a milk protein and emulsifier, interacts with capsaicin and prevents binding to TRPV1.

Sweetness has also been shown to reduce chilli burn, the mechanism for this is not well understood but it could be that there is a chemosensory link between sweetness receptors and TRPV1.

How to Fix an Over-Spiced Dish in the Kitchen

This science can also help us out a bit when trying to fix an over-spiced dish.

If you’ve added too much chilli, my first move would be to add some milk or yogurt. By adding milk or yogurt some of the capsaicin in your dish will be bound to casein which means it wont bind to your TRPV1 receptor. Luckily, casein is heat-resistant and will generally survive the cooking process.

Other fats and oil might work as well, capsaicin will be dissolved in the fatty part of the food and may be less likely to interact with TRPV1.

Adding more fats and oils isn’t normally something you want to do but butter could work and in things like Thai curries you could add more coconut milk.

Finally, as we saw above, sweetness helps reduce chilli burn so add some sugar.

Can You Build a Tolerance to Spicy Food? (Desensitisation and Tachyphylaxis)

The picture I’ve painted of capsaicin so far is pretty simple, it triggers pain receptors and that’s why it burns. But like most things in biology the full story is much more complicated.

As any chilli eater knows you seem to get better at eating chilli over time and there is a biological basis to this.

From the very first mouthful of spicy curry, biochemical process are triggered that immediately start reducing TRPV1s sensitivity to capsaicin.

When TRPV1 is activated the receptor cell sends the “I’m burning” message but it then makes it harder to send the message again. This is a common mechanism in neurons to avoid excessive receptor stimulation.

This rapid and transient desensitisation doesn’t seem to help me that much when eating spicy food though. But a more long term resistance can be built up because of a phenomenon called tachyphylaxis.

Capsaicin and Tachyphylaxis.

Tachyphylaxis is a pharmacological term for when a drug rapidly stops working after either a single high dose or after repeated doses of the same concentration.

If you start eating a lot of chillies you are effectively dosing yourself repeatedly with capsaicin. When this happens TRPV1 receptors become desensitised to capsaicin and this desensitisation can last for days or even months.

Why this happens with capsaicin is poorly understood but it has led, paradoxically, to a lot of interest in capsaicin as a treatment for chronic pain, especially for neuropathic pain (pain caused by damage to the nervous system).

For chilli eaters though it explains why we can get better at eating spicy food over time. If you regularly eat spicy food you’ll induce tachyphylaxis to capsaicin and be able to eat spicy food with less discomfort.

Why Do Humans Enjoy Painful Food?

This leaves just one question. Why do humans like eating chillies even though they do horrible things to us?

I’d love to say I have an answer to this but the science is inconclusive. There are plenty of theories though.

Some theories focus on human psychology. For example we eat chillies as way of expressing machismo, anyone who has seen professional chilli eating competitions or even drunk friends daring each other to eat hot chillies would agree with this.

Similarly, there is an idea that eating chillies is low-risk ‘risk-taking’ behaviour. There have been studies that suggest that chilli consumption is highest amongst those with sensation seeking personality traits (you can read one of these studies here).

Other theories focus on physiological factors. The sweating caused by capsaicin could have driven the popularity of chillies in hotter climates (the ‘capsaicin-as-air-conditioning’ theory).

Consumption of capsaicin also causes endorphin release as part of the bodies response to perceived tissue damage. Endorphins target opioid receptors, the same receptors targeted by heroin and morphine, and could thus provide a natural high that could drive a continuing fondness for chillies (the ‘capsaicin-as-a-drug’ theory).

Yet other theories suggest that the mild anti-microbial activity of capsaicin may have provided a way of preserving food (the ‘capsaicin-as-a-refrigerator’ theory).

Finally, it has been suggested that inflammation in the mouth, again caused by the bodies response to perceived tissue damage, could make the oral cavity more sensitive to other sensations.

This could make eating a spicy dish more intense as our sensation of the other ingredients such as salt, acid, alcohol and carbonation is increased.

Our mouth becomes so sensitive that it makes, as Harold McGee puts it, ‘inhaling room-temperature air like a refreshingly cool breeze’.

None of these theories explain everything and some of them explain very little so I suspect it’s a combination of the individual and a whole bunch of different factors that contribute to our love of chillies.

From a genetic viewpoint about 18-50% of the variation in capsaicin sensitivity in humans can be explained by the genetics of the individual so those who really like chillies might just be genetically predisposed to liking them.

We don’t really know to be honest. The only thing we do know is that we complicated, boastful and confused humans will continue eating chillies for as long as there are chillies.