Mind & Body

Here's Why Wounds Heal Faster in the Daytime

There are a lot of ailments you can sleep off: a bad mood, a hangover, and, you know ... sleepiness. But according to a new study, one thing it's hard to sleep off is a skin injury. The best time for healing is broad daylight.

Related Video: Your Biological Clock at Work

Skin Has Circadian Rhythms, Too

To explain why this is, we have to first back up and talk about circadian rhythms. Also known as your internal clock, your circadian rhythm is powerful. When you mess with it —through irregular sleep, for example — you get jet lag in the short term and a higher risk for cardiac disease and diabetes in the long term.

Circadian rhythm originates in the brain — the hypothalamus, to be exact — but it has effects throughout the body. For instance, your internal clock affects the size of your liver. (Seriously: Your liver detectably inflates by day and deflates by night.)

Your circadian rhythm also affects your largest organ: the skin. Specifically, it affects fibroblast cells, according to a study by Cambridge researchers. These cells function sort of like traveling doctors; when skin is broken, they head over to the wound to produce collagen and other skin-repairing proteins.

To travel through your body, though, fibroblasts rely on a protein called actin — and it's more available by day than by night. It's unclear why this is, exactly, but one theory says our defenses against injury ebb and flow with the likelihood we'll hurt ourselves. Since people are more active (and therefore more injury-prone) in the day, that's when our bodies have evolved their defenses to be strongest.

Ready, Set ... Heal!

To explore this phenomenon, researchers studied both skin cell cultures and living mice, timing how quickly they healed from wounds. They found that actin was more available and fibroblasts worked faster when skin abrasions happened in daylight conditions. In fact, by day, they found that daytime injuries healed roughly twice as fast as at night.

They found a similar result when they looked at humans. When they analyzed data on accidental burn victims, they found that people who got burned at night (between 8 p.m. and 8 a.m.) took 60 percent longer to heal than people burned during the day. Healing took an average of 27 days for nighttime burns and 17 days for daytime ones.

This might seem like a random fact to focus on — it's hard to control when you accidentally burn yourself! — but it actually has major implications. First of all, not all skin wounds are accidental. Surgeons make purposeful incisions all the time, and this new insight into fibroblasts can help them optimize their surgical procedures.

Even more importantly, skin doesn't heal faster during actual daytime — just during what our body perceives as daytime. As this military-tested jet-lag cure indicates, people can modify their circadian rhythms through dietary tricks; in this Cambridge study, researchers also found that lighting and medication can achieve similar effects. There's still no way to make surgery fun, but at least now, doctors know that tweaking patients' circadian rhythms could speed their recovery.

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Discover more ways your internal clock controls your life — and how to take that control back — in "The Circadian Code: Lose Weight, Supercharge Your Energy, and Transform Your Health from Morning to Midnight" by researcher Dr. Satchin Panda. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Mae Rice January 7, 2019

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