What Causes Pupils to Dilate?

BlueyeDilated pupils (also referred to as mydriasis) can occur for a wide variety of reasons. Normally, the pupil will dilate in dim lighting as an attempt to increase the range and quality of your vision. When your surroundings become less dark, the pupil shrinks back to a smaller size in an effort to protect the eye from damage caused by excessive glare. In essence, the brightness of the environment is a large factor in determining the size of pupils on an everyday basis. Sometimes, however, pupils become dilated in a light-filled environment for the following common reasons:


Although the exact reasons are still unknown, it is been found that our eyes will dilate when we find something attractive. This can be anything: a car, house, or people we find to be romantic interests. Basically, anything that our brains find to be interesting will subconsciously result in dilated pupils. Interestingly enough, things that our brain does not find interesting or attractive often shrink our pupils even further.

Furthermore, when it comes to individuals we are romantically drawn to, we are more likely to find someone attractive if their eyes are currently dilated. In numerous studies this was found to be true. Most famously, in a study conducted by Eckhard Hess they showed men pictures of women, and vice versa; they asked them whether they thought the person in that photograph was attractive. It was concluded that more often than not, the men and women both picked the members of the opposite sex with dilated pupils to be more attractive.


5854670985_167f1f2998_zIn an instance of trauma or brain injury, the pupils can become abnormally dilated. This is because the muscle responsible for maintaining the size of the pupils (iris sphincter) can fail to send certain signals to the brain; this can be seen when someone suffers a concussion or a stroke. Also, the iris sphincter itself can become damaged and as a result will fail to do its job of keeping the pupil at a healthy size.

If someone receives any sort of blow to the head, and their pupils grow abnormally large, it is best to have them see a doctor as dilated pupils can be a sign for more serious problems.


Blue_and_Red_Pills_(Cold_Pills_and_Decongestants) To understand why drugs often dilate the pupils, it is important to know that there are two “branches” of the brain: the sympathetic nerves system and the parasympathetic nervous system. The former is responsible for the “fight or flight” emotions and essentially speeds up the body; the latter slows it down.

When the pupils are dilated because of drug use, it means the substance has sped up the sympathetic nervous system and the body falsely enters into “fight” mode. A side effect of that reaction is dilated pupils.

Common drugs that often make the pupils dilate are: marijuana, amphetamines, cocaine, ecstasy and LSD.

By itself, eye dilation is usually just a reaction to the amount of light present and is not considered to be dangerous or unhealthy. It’s when the dilation is the result of injury or a substance put into the body that the problems can start to occur. If your eyes remain dilated for an extended period of time for a reason other than a reaction to the current brightness, it is recommended that you go see a doctor or health professional. 

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