Why are 100% blackout sleep masks important for REM Sleep?

Let's break down the stages of sleep so you understand better what REM sleep entails! So sleep is defined by 3 stages. The 1st stage, you drift off which is usually light and can have some moments of consciousness, such that people will report being awake if you nudge them ("I was just resting my eyes.")

You then go into much deeper stages of sleep, 2nd stage (no dreams, easy to wake up) and then 3rd stage (deepest sleep, most important and refreshing, can dream a little but boring/ordinary.)

Then REM sleep happens, then you either wake briefly or go back into another cycle of 1-2-3-REM. These cycles last about 1.5-2 hours and happen through the night.

Going from deep sleep, the brain switches EEG patterns to looking more like you're awake, but all your muscles shut off, and all your neurons that use serotonin, norepinephrine, and histamine stop firing completely, with a big shift towards acetylcholine-using neurons. Your eyes start to move intermittently (hence the name, "rapid eye movement" otherwise known as REM or REM Sleep) and your heart rate, temperature, breathing, and blood pressure get irregular. Most dreams, especially those vivid and weird dreams, happen in this stage.

REM sleep is when the brain is most active, performing critical functions like memory consolidation and "housekeeping" of the brain- plus a whole host of biochemical functions we still don't fully understand. The current best explanation for REM sleep relates to the body having a chance to get rid of waste products in the brain, likened to how you need to shut down a restaurant and put up the chairs to clean everything. 

You do need sleep for memory to work right. While non-REM sleep seems to be important for declarative memory (facts and memories of things that happened, like names/dates or your last vacation), REM sleep seems to be important for procedural memory (learning to do things, like ride a bike or learning a new language.)

This is simply due to the effects of light pollution. Light terribly suppresses the production of natural melatonin in your body.

This is because light pollution, whether from your endless doom scrolling or other external sources, throws off your body’s circadian rhythm. The circadian rhythm (your internal body clock which follows a 24-hour cycle) plays a huge role in your body's health and overall mental and physical performance. As you're struggling to hit all the sleep stages including REM sleep, your ability to recharge and get the required proper sleep reduces.

Sleep masks help you experience a more restful slumber by getting you proper REM sleep. With less light disturbing your sleep, this, in turn, helps you focus during the day, boost your mental and physical energy and mood, improve your short-term memory, and more!

Studies have revealed that there was a drastic difference between the levels of cortisol and melatonin between those who slept with sleep masks and those who did not. Melatonin and cortisol are both key biological markers of our circadian rhythm. Melatonin is an important circadian regulatory hormone. Meanwhile, cortisol plays a key role in helping our bodies cope with stress and also helping to regulate our metabolism. 

According to a study published in Oxford Academic, sleepers who went to bed with eye masks experienced improved alertness and memory likely linked to stronger REM sleep. The study also confirmed that those who wore sleep masks experienced an increase in the length of their REM sleep cycle.

(1) “Wearing an eye mask during overnight sleep improves episodic learning and alertness” Oxford Academic, academic.oup.com/sleep/article/46/3/zsac305/6912219. Accessed 22 October 2024.