In 2017 the Nobel Prize in Physiology or Medicine went to Jeffrey Hall, Michael Rosbash and Michael Young. They had worked out the molecular mechanism behind the body's circadian clock, and they did it by studying a gene called period in fruit flies. Their work is about how living things keep time. It is not about face cream, and I want to be clear about that. But it is the reason I take the phrase skin repairs at night a little more seriously than I used to, and it is what a bottle called Midnight is quietly leaning on.

L'Oréal Paris makes that bottle, and the brand has an odd origin for a drugstore giant: a young chemist named Eugène Schueller, who launched his first hair dyes in 1907. A century later the same house sells the Age Perfect Cell Renewal Midnight Cream, and the useful thing to know is what it is. L'Oréal describes the loreal midnight cream as a barrier-restoring night cream for thin or fragile skin, and says it repairs the skin barrier up to 1.5 times faster. It is fragrance-free in one version and paraben-free, and it is made for mature skin, applied to a cleansed face and neck at night. It is not a retinol. The name is the honest bit: it is a comfort cream.

The trick is to see where it sits in the wider L'Oréal Paris line. The Revitalift Triple Power Rich Night Moisturizer and the Revitalift Anti-Wrinkle + Firming Night Cream are the other night options in the same grid, and the Collagen Moisture Filler Day Night Cream is the one you can wear around the clock. For mornings, the Age Perfect Cell Renewal Day Moisturizer with SPF 25, the Revitalift Anti-Wrinkle + Firming Day Cream SPF 25 and the Triple Power Face and Neck Moisturizer SPF 30 give you sun protection, and the Triple Power Anti-Aging Face Moisturizer is the everyday one.

One rule for eye products: use the smallest amount that seems reasonable, then dot it on the bone rather than dragging it across the lid. Anything that travels does not need to be a large quantity.

The matching piece for Midnight is the Age Perfect Cell Renewal Midnight Eye Cream, which is the sensible pairing if you already like the face version. The Revitalift Anti-Wrinkle + Firming Eye Cream is the Revitalift equivalent, and the Revitalift 2.5% Hyaluronic Acid + Caffeine Under Eye Serum is the lighter, thinner option for morning.

For serums, the Revitalift 1.5% Pure Hyaluronic Acid Serum is the simplest place to begin. The Vitamin C Vitamin E Salicylic Acid Serum is the more active one, and Age Perfect Serum Le Duo comes as a pair. The Revitalift Melasyl Dark Spot Creamy Serum is the one to consider if marks are your main complaint.

The Revitalift Derm Intensives Night Serum with 0.3% Pure Retinol is where the caution goes. The American Academy of Dermatology says retinoids should not be used during pregnancy, should go on at night with sunscreen in the daytime, and can be started every other night. Cleveland Clinic recommends a patch test first and notes that retinol raises the risk of sunburn.

A pairing I like: a hyaluronic serum on damp skin, then the Midnight Cream on top. Save the retinol for alternate nights, never the same evening as a strong acid.

What I would skip: a retinol serum the night before a beach trip. Give your skin a week without it.

Start by asking what you want the cream to do while you sleep, because the answer changes the shortlist. Comfort, firmness and barrier support are three different jobs, and most night creams are good at one of them.

For comfort, Kiehl's Midnight Recovery Omega-Rich Cloud Night Cream is the obvious neighbor of the L'Oréal one, sharing the word in the name. First Aid Beauty's Ultra Repair Firming Night Cream, with colloidal oatmeal and niacinamide, is the sensitive-skin option. Biossance's Ectoin Overnight Rescue Deep Repair Night Moisturizer with squalane is another gentle pick, and Yepoda's The Midnight Magic is the rich overnight cream with ceramides.

For barrier and firmness, Medik8's Advanced Night Ceramide Age-Defying Night Cream is the more clinical bottle. Origins' Plantscription Youth-Renewing Power Night Cream is the anti-aging one, and Clarins' Multi-Active Night Moisturizer for lines, pores and glow with niacinamide is the multitasker. Fresh's Lotus Youth Preserve Radiance Renewal Night Cream is the glow-first pick.

A pairing I like: the same night cream for a month, and a different serum underneath if you want a change. It keeps the experiment readable.

What I would skip: adding a new night cream in the same week as a new retinol. If skin turns red, you will not know which one to blame.

Try this on a night when your skin feels parched: apply your usual night cream, then smooth a thin layer of a sleeping mask over the top. It is a small change that shows you the difference between a cream and a mask better than any label.

LANEIGE's Water Sleeping Mask for Moisture Barrier Support is the one I would reach for first. Sephora Collection's Quenching Sleeping Mask and belif's Aqua Bomb Sleeping Mask are the hydration-first ones. Hanyul's Yuja Brightening Sleeping Mask & Moisturizer combines both jobs, and Clinique's Moisture Surge Overnight Face Mask and Origins' Drink Up Intensive Overnight Hydrating Face Mask are the two I would give to a friend who wakes up with tight skin.

OLEHENRIKSEN's Après Skin Overnight Moisturizer + Mask and Kiehl's Ultra Facial Overnight Cream Hydrating Mask with 10.5% Squalane are the richer options, the kind you want on a winter night.

A pairing I like: a sleeping mask on two or three nights a week and a proper night cream on the others. Skin does not need the same thing every night.

What I would skip: a heavy sleeping cream after a strong exfoliating acid. Let the skin settle first.

I think the Midnight Cream is best understood as a soft landing at the end of the day, not a treatment, and that is a fine thing to be. If your skin is thin, dry or a little worn out, start there. If you want active ingredients, add a serum on other nights.

Apply it to a clean face, a few minutes before you turn off the light. Hall, Rosbash and Young found the clock in a fruit fly. You only have to remember to show up to it. Dim the lights, wash your face and let the cream do the quiet part. If you want to keep browsing, I also put together Maëlys Names Every Cream After the Body Part It Is Meant For and Clinique Moisture Surge, the 1988 Gel-Cream That Keeps Being Rewritten.