When you sleep with your boyfriend or your girlfriend, chances are you guys will share the same bed, inevitably sharing the same comforter. A sleep scientist at Penn State, Daniel Gartenberg, Ph.D., argues against sharing a comforter.

Sharing a comforter can possibly put you out of rapid eye movement (REM) sleep and put you into a non-rapid eye movement (non-REM) sleep, a lighter sleep stage, consequently reducing your quality of sleep. REM sleep is a crucial restorative stage that has implications in learning and memory. In REM sleep, however, your body does not participate in thermoregulation and it cannot regulate its body temperature by sweating when it's hot or shivering when it is cold. As a result, if the sleeping environment becomes too hot or too cold, you may consequently spend most of your sleep in non-REM sleep.

Generally, men have a higher body temperature than women, but there are always exceptions. A comforter may be perfect for you and keep you in REM sleep for long period of time, but the same comforter may be unfit for your partner, keeping them out of REM sleep.

The optimal temperature appears to be "between 68 and 72 degrees Fahrenheit" and "temperatures above 75 or below 54 can disrupt sleep," according to Michael J. Breus Ph.D., a Board Certified Sleep Specialist (with a twitter handle, @thesleepdoctor), who wrote Good Night: The Sleep Doctor's 4-Week Program to Better Sleep.

A study in 2014 has also shown that colder sleeping environments may lead to benefits in metabolism through expansion of brown fat tissues. Brown fat tissues appear to help the body with heat regulation and perhaps weight loss. Five healthy male volunteers underwent four consecutive months of sleeping in "temperature-controlled research facility" at the National Institute of Health Clinical Research Center. The temperature of the room in which the volunteers slept in changed monthly from neutral (24°C / 75.2°F), cold (19 °C / 66.2°F), neutral (24°C / 75.2°F), then hot (27°C / 80.6°F). At the end of each month, metabolic tests were performed. The results showed that the tests following the cold sleeping environment indicated doubled volume of brown fat tissues in addition to sensitivity to insulin, which may both be perceived as metabolic benefits.

This is not to say that you shouldn't sleep with your partner…but maybe investing in an extra comforter may benefit both of you substantially.