The Power of Overnight Repair Serums for Winter Skin

"Overnight repair" is on a lot of labels. Here is what night really changes in your skin, which claims are overstated, and what a good bedtime routine does.

What Changes After Dark

Skin has a daily rhythm. In a study of 16 volunteers sampled every two hours over 24 hours, transepidermal water loss, surface pH and temperature all followed a circadian pattern, and the authors concluded that skin permeability is higher in the evening and at night than in the morning^[1]. A separate study found that barrier recovery after tape stripping was slowest between 8 pm and 11 pm, and that skin temperature and basal water loss peaked at about 3 am^[2]. Both are small studies, and the second came from a cosmetics company's research center (Shiseido).

Put simply, the hours when you are asleep are the hours when skin loses water most easily. That is the real case for what you do before bed. For the full picture on night routines, see our earlier post on night serums.

One Claim to Treat With Care: "Skin Renews Itself at Night"

You will often see this on labels. The picture is more complicated. In mouse skin, the cell-division phase (S-phase) peaks at night, and mice are most sensitive to UV-induced DNA damage at night. The same paper notes that in human epidermis the largest number of cells go through S-phase in the late afternoon^[3]. A human study of skin and oral mucosa biopsies found the clock genes working in skin, and a marker of DNA synthesis in oral mucosa peaking in early afternoon^[4]. So "your skin rebuilds while you sleep" is not what these human data show. What is better supported is the water-loss and barrier-recovery rhythm above, and the effect of sleep itself.

Sleep Matters More Than Any Serum

In a study of 60 women, those who slept poorly (five hours or less) had higher baseline water loss, and 72 hours after tape stripping the good sleepers had 30% greater barrier recovery^[5]. All were healthy Caucasian women, so it may not translate to every skin type. In 11 women, a single night of sleep deprivation delayed barrier recovery in a separate experiment^[6]. Both are small and show association, but they point the same way. Our post on sleep and skin covers this in more depth.

What an Overnight Routine Can Do

If night is when skin loses water most easily, a good bedtime routine does two things: it puts water in, and it keeps it from leaving. Reviews describe basic moisturizers as combining humectants, which attract water, with occlusives such as petrolatum, which slow its loss^[7]. Bedroom air matters too, because low humidity reduces barrier function and makes skin more reactive^[8]. So it is worth keeping an eye on how dry your bedroom air gets when a heater runs.

A Simple Overnight Routine

• Cleanse thoroughly but gently, since sunscreen and city grime need to come off.
• Apply a hydrating serum to slightly damp skin.
• Follow with a moisturizer, and a thin occlusive on any cracked or very dry patches.
• Keep strong actives for the nights your skin is calm, and use only one at a time.
• If you use a heater, keep the room from becoming very dry, and keep a regular sleep time.