What does it mean when your pupils dilate?

Have you ever noticed someone’s pupils dilating? Or perhaps you’ve looked into the mirror and watched what your own pupils do?

There are lots of stories about exactly what your pupils are telling the world – does an increase in size mean you’re attracted to someone? Maybe it means you’re tired? Then again, maybe you’re just adjusting to the light!

Well, you don’t have to wonder anymore! We’ll dip into science and psychology to sort the fact from the fiction and explore exactly what it is that makes your pupils dilate…

Our eyes are incredible

Our eyes are truly amazing, in fact, they’re second only to our brains as the most complex part of our bodies.

When you consider how close they are to our brains and the complexity of the optic nerve that runs between the two, you start to appreciate quite how connected they are – so much so that many fields of science actually consider them a part of the brain – the brain’s interface with the world.

With this in mind, it’s no wonder people refer to them as the ‘window to the soul’ – they seem to indicate so much about what we’re thinking, our mood, whether or not we’re telling the truth, whether we feel guilty about something – and much more.

The pupils

The pupil might look like a black spot on the surface of the eye – but it’s actually a hole that expands and contracts to vary the amount of light that reaches the sensors at the back of the eye that are connected to the optic nerve.

The wider part of the eye actually contains muscle tissue that causes this hole to open and close – but it’s not just light that it responds to. In fact, there are around 9 significant things that can cause your pupil to open and close.

Let’s take a look at each in a little more detail:

A person’s level of attraction

It turns out that the most commonly considered reason for your pupils to dilate is true! The level of attraction a person feels toward another person is likely to be reflected in the size of their pupils.

So, next time you look into your loved one’s eyes and you see their pupils expand you can probably take it as a compliment – that said, if your relationship can be a little volatile, you might want to consider the next reason on the list…


 Becoming angry causes our brain to release hormones that ready us for confrontation or even physical aggression. While it’s unlikely that we’re going to end up in a fight each time we get annoyed, that doesn’t stop the process – and part of that process is increasing our ‘alertness’.

When we’re in this state, even slightly, our pupils dilate to make sure we’re taking in as much of our surroundings as possible, readying us for whatever might occur.


 In much of a similar way to the anger response, an interested brain also expands the eye’s pupils to take it as much information as possible.

Interestingly though, it doesn’t have to be visual information that the brain is trying to collect – an interesting speech, podcast or audio book will often cause the pupils dilate, even though the stimulus is coming via the ears.


 Okay, disgust shouldn’t really have a place on this list as it actually causes the pupils to contract rather than expand – but it’s another example of how our psychology and behaviour impacts our eyes.

When faced with an image or experience we don’t like, the pupils contact to limit the amount of information we can take in – but it’s subjective. Where a coroner might be interested at certain points of his or her job, a more general member of the public is likely to be disgusted – meaning the person’s attitude toward a situation dictates the eye’s response.


 If we experience pain our pupils dilate – and it’s perhaps an effect that’s related to point number 2 on this list – anger. While pain, or whatever’s caused it, might not make us angry – it’s possible our brain is looking for the source of that pain – and preparing us for defensive reaction toward it.

A hardworking or stressed brain

 Our brains have an optimum working capacity – and every task that requires some thought adds to that workload.

Stress’ comes at a different level for everyone – but wherever your limit lies your pupils are likely to show it – as the harder your brain works the more dilated they’ll become. Again, this is likely to be an attempt to gather as much information as possible – in an effort to make your task as manageable as it can be.

Personal opinion

 Opinion has a big impact on our pupil’s reaction to stimulus – the more we like or agree with someone or something the more our pupils will dilate.

Show a sport’s fan an image of an opposing team or player and their pupils will contract, however, show them the team or player they support and you’ll see their pupils expand. Then, show the same images to an opposing fan – and you’ll see the opposite occur…


 Although our brains are powerful – medication can completely override almost all of the functions that control the eye’s response to stimulus.

While drug use is commonly cited as a reason that pupils dilate or contract, many prescription medicines can have the same effect; antihistamines, decongestants, anti-sickness tablets and some anti-depressants can make the pupils expand.

Illegal drugs like MDMA (ecstasy), cocaine, amphetamines and some hallucinogens can also make the pupils dilate or constrict significantly too – and checking the eyes with a torch is a common first step for police who are trying to ascertain whether or not someone is under the influence of narcotics.

Head injury

 Unfortunately, a head injury can have a huge impact on the communication between the brain and the eyes – leading in some cases to a loss of control over pupil movement altogether.

If you’ve ever been assessed for concussion, you’ll know that your pupils get a lot of attention from medical staff, they generally looking for a normal reaction to light – and checking that your pupils are equal in size and still round. Any sign that they’re permanently dilated or unequal could indicate lasting damage.

 So, what’s the most common reason your pupils dilate?

As you can now tell, pupils are deeply connected to our brain – not only from a function point of view, but also psychologically – what causes one person’s pupils to dilate might cause the total opposite in someone else.

There are no hard and fast rules about what’s causing pupil dilation – but if you’re seeing it or experiencing it, you might want to scan over this list again and consider which is most likely to be true in that moment!

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