We've all been there: rolling around on the bed, tossing right, then left... wide awake. Not even counting sheep — 1,000 or more — does the trick.

It could be the stress of an upcoming exam, too much coffee or there might be countless other reasons for why you can't fall asleep.

It might just be the light. Sure, some people can fall asleep with the lights on. But did you know that light can affect the quality of your sleep and even your mental performance the next day?

Is sleeping with an eye mask good for memory?

A study published in the journal Sleep suggests that wearing an eye mask at night could improve memory and alertness the next day.

It describes how participants in the study performed better in visual memory and vigilance tests when they spent more time in a key stage of sleep called slow-wave sleep.

Slow-wave sleep (SWS) is a deep sleep stage where you sleep like a rock, and don't wake easily. It is also a phase during which some people talk or sleep walk. SWS plays an important role both in our ability to store long-term memories and also in our memory function the next day.

There are many things that researchers don't know about sleep but what is clear is that it fulfils an essential function for maintaining our mental, physical and emotional well-being. Poor sleep quality can be very harmful and lead to immune system and heart problems, mental impairments or metabolic disorders.

Sleep study finds improved cognitive performance

The study involved 122 young adults between the ages of 18 and 35, who were divided across two experiments.

One week-long experiment focused on studying the participants' mental performance, while the other four-night-long study focused on studying brain activity during sleep.

Participants either slept with a regular eye mask or with a so-called "control" eye mask that had holes over the eyes so that it did not block the light.

The masks with holes were used as a means to check whether it was the light-blocking capacity of eye masks, rather than the masks themselves, that was behind their effects.

To measure memory performance, the researchers used a test called paired associates learning. For alertness, they used a psychomotor vigilance task to measure the participants' reaction time. 

They found significant increased memory performance and faster reaction times among participants who slept with eye masks compared to those who slept with the control mask.

They also measured motor-skills learning tasks with different tests, like typing numbers on a keyboard with the non-dominant hand, but found no differences between the two groups.

Brain waves were measured on 33 participants using a wearable EEG-device to look for differences in the duration of their SWS stages depending on whether they used the normal eye mask or the control one. The results showed that participants wearing conventional eye masks performed better on the memory test, the longer their SWS stage.

The sleep study was relatively small

Only 89 people participated in the first study and in the second, it was 33, which is relatively small. So it's hard to draw general conclusions from the findings. Larger sample sizes would be more representative and provide more reliable results.

In addition, the study only included people aged between 18 and 35 years, so we don't know whether wearing eye masks is beneficial for other age groups.

Participants wore eye masks for a week or less, so we don't know how long the effects could last and whether they may wane with time or not.

Moreover, the study only examined healthy adults without sleep disorder and thus the findings may not necessarily apply to other people, such as those with sleep disorders or other conditions.

But do face masks work?

Some people don't like the feeling of wearing an eye mask and find them uncomfortable, some say they have never slept better.

But we do know that our sleep-wake cycle is regulated by light or the absence of light. 

We need dark to get a good night's sleep because that's when our body releases melatonin, the sleep hormone. Light inhibits the production of melatonin and prevents us from falling asleep.

This becomes tricky at higher latitudes, in countries where seasons are more pronounced and during summer you may experience virtually no night at all.

So, the effects of light in sleep have been well studied and eye masks offer a cheap and easy way to block light without the side effects of sleeping drugs. 

Eye masks have also been found to significantly improve sleep quality among patients in intensive care units.

But more research is still necessary to better understand whether the benefits apply to other groups of people and how long they last. 

Edited by: Carla Bleiker, Zulfikar Abbany