Dear Dr. Universe: How do bags form under your eyes? — Sophia Ivy, 7, New Providence, N.J.

Dear Sophia Ivy,

If you’ve ever stayed up late and woke up really early, you may have noticed a little puffiness or swelling under your eyes.

When I asked my friend Devon Hansen about the answer to your question, she said that we first have to know a bit about how sleep works.

Hansen is a researcher at Washington State University and is very curious about sleep. She told me that the main way our sleep is regulated is through something called the circadian rhythm. You can think of it kind of like a 24-hour clock that helps run all the systems in your body, including sleep.

This system is actually controlled by light. Our ability to sense light is part of the reason why humans are awake and alert during the day. And when it’s dark out, we go to sleep.

It turns out that all the organs in our bodies are actually regulated by this circadian rhythm. That includes the biggest organ of them all: the skin.

Some scientists who have studied sleep have found that if you sleep poorly, your skin is not able to function as well. That is, it’s harder for your body to recover from being exposed to the outside environment, regulate your temperature, and stay hydrated.

While we don’t know all the details when it comes to exactly how these bags form the way they do, it’s likely that sleeping poorly has the ability to change the way your skin looks. That may include those bags, or even dark circles that form underneath the eyes.

You might even feel a little heaviness around your eyes when you are really tired. It’s kind of like how the rest of the muscles in your body get tired after you use them a lot.

It’s important to get a good night’s rest to make sure all your organs can stay healthy. Kids who are about five to ten years old usually need about 10 to 11 hours of sleep. And like grown-ups, 10- to 17-year-olds need about eight to nine and a half hours a night.

While sleep is one of the main reasons we see bags forming under people’s eyes, there are also some other reasons. It might be partly genetic or your skin tone might just make them more obvious. We also see people get bags under their eyes when they have allergies or as they start to age.

As the body ages, the tissues around the eyes sometimes start to get a little weaker. The skin under our eyes is pretty thin and the blood vessels can sometimes stand out, making the bags a bit darker that they used to be.

So, a bit of puffiness under the eyes could be a sign that you are maybe a bit wiser than you once were — or that maybe you just need a little cat nap.

Sincerely,

Dr. Universe