How staying up late leads to dark circles and hair loss

Contribution unit: Chongqing Association of Science Writers

Author: Li Siqi, undergraduate student in Clinical Medicine, Class of 2024, Chongqing Medical University.

Supervisor: Associate Professor Xu Lei from the Department of Immunology and Pathogen Biology at Chongqing Medical University, Director Technician Zou Jingbo from the Red Cross Volunteer Service Team for Health Promotion in Yongchuan District, Chongqing (Zou’s Science Popularization Garden).

Review Expert: Li Hanbin

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"Involution" has almost become a shared experience for everyone around us. It’s hard to pinpoint when exactly staying up late became our norm. We find ourselves unwilling to sleep at bedtime and struggling to wake up in the morning — starting from initially staying up late because we had unfinished work, to later choosing to do so, leading to difficulties in falling asleep or even insomnia. As people often joke, "The night will not spare those who stay up late; it will gift you dark circles, make you burn the midnight oil, rob you of sleep, and cause you to lose the most hair."

So, what exactly happens to our body during those few hours of staying up late?

Imagine it is now 11 PM. The dark night, the silence outside the window, and your body’s "command center"—the hypothalamus—are all issuing commands for sleep, reminding you that it's time to rest. At this moment, you may feel your eyelids growing heavy and your eyes dry, but you remain unfazed, focused on your own world, keeping your brain in a state of excitement.

From 11 PM to 1 AM is what Traditional Chinese Medicine refers to as "Zi Shi," which is also the first golden period of sleep. From the perspective of Western medicine, this is a critical time for the liver to metabolize toxins and undergo self-repair. If one does not sleep during this time, the liver's detoxification cells cannot function properly, resulting in the accumulation of toxins in the body.

From midnight to 2 AM, the stomach and brain that should be resting are confused by your wakefulness. The stomach continues to secrete ghrelin, causing the brain's craving for high-calorie food to reach its peak. At this point, you need to exert more effort than during the day to resist the temptations of barbecue and fried chicken. Moreover, the convenience of takeaway services has removed the final barrier. Thus, having a late-night snack seems only natural.

However, after eating, the body's insulin is forced to "work overtime," which encourages body cells to absorb sugar from the blood. As this happens repeatedly, the cells gradually become less sensitive to insulin and no longer effectively absorb sugar. Glucose has nowhere to go and ends up lingering in the bloodstream, laying the groundwork for the development of diabetes.

Between 2 AM and 4 AM, you should ideally be in deep sleep, experiencing rapid eye movement and dreaming. During this time, the cerebrospinal fluid in the brain and spinal cord washes over the brain like waves, clearing away metabolic waste such as accumulated beta-amyloid from the day—substances that may be related to Alzheimer's disease.

But if you haven't fallen asleep by this time, your brain cannot enter deep sleep and instead remains immersed in metabolic waste. As a result, the next day you will feel dizzy and lethargic, with a noticeable decline in memory; things you just learned will slip your mind as if the classic line were echoing: "What was that name again?"

From 4 to 6 in the morning, you still haven’t fallen asleep. The cortisol, which is responsible for waking the body and should naturally surge at this time, is disrupted due to staying up all night. As a result, when you should be getting up, you feel drowsy, and when you need to focus, you are utterly exhausted, drastically reducing your efficiency in both life and work. Meanwhile, the secretion of collagen in your skin decreases, and the next day, when you look in the mirror, your complexion appears dull, your pores enlarged, and the dark circles under your eyes are glaringly apparent, making makeup only a half-hearted attempt at concealment.

Therefore, sleep is by no means as simple as just closing and opening the eyes; it is actually the body's "invisible repairman." Staying up late, on the other hand, is like borrowing energy from the next day, sacrificing long-term health and future quality of life for a moment of wakefulness. Prolonged sleep deprivation can lead not only to temporary weight gain and memory decline but also to serious diseases such as myocardial infarction, Alzheimer's disease, depression, and cancer.

However, you don't need to worry excessively. Staying up late occasionally is like going through a brief "storm"; after that, calm will always return. Our robust bodies have remarkable repair and compensation abilities. As long as we quickly return to a regular sleep schedule, our bodies are fully capable of clearing up the "mess" and minimizing any short-term effects.

Similarly, there is no need to constantly worry about the effects of insomnia. If you simply close your eyes and lie quietly at night, even without falling asleep quickly, your body has already entered a "standby" state. This form of rest can alleviate some fatigue by itself. Therefore, occasional difficulties in falling asleep, as long as they do not lead to anxiety, actually have a limited impact on the following day. The combination of "staying up late + anxiety" is often the most damaging to the body.

In general, our bodies can tolerate occasional disruptions, but they fear long-term chaos. Instead of panicking over a single night of staying up late, it’s better to focus on establishing a regular daily routine. Once you understand the grand and intricate repair work that occurs at night, you may feel a sense of awe. So, on the next night, willingly turn off the lights and allow your body—this complex and magnificent city—to have a quiet and complete "maintenance night."