The Routine, In Order

Four things have evidence behind them. Everything else is optional. What to apply, in what order, and why consistency beats every other variable.

There is an inverse relationship in skincare between the number of steps a woman performs and the likelihood that she is still performing them in a year.

Which matters more than any individual product, because every piece of evidence supporting daily skincare was generated on people who kept going. The four-year retinoid studies measured women who applied a retinoid for four years. The vitamin C absorption data describes a reservoir that depletes with a half-life of about four days. Nothing in the literature supports a routine you abandon in March.

So the useful question is not what the optimal routine looks like. It is what the optimal routine you will still be doing next winter looks like, which is a considerably shorter list.

Four things have evidence

Sun protection, every morning, which is the highest-return item at any age. Most visible ageing on exposed skin traces to ultraviolet exposure, and most of a lifetime dose arrives incidentally rather than on holiday: through the car window, at a desk, on grey days.

A retinoid, at night, at whatever frequency you tolerate. This is the strongest evidence base in topical skincare. A 1993 New England Journal of Medicine study compared sun-exposed forearm skin against lifelong-protected buttock skin in twenty-six people and found the exposed skin producing fifty-six percent less collagen. In its treatment arm, ten to twelve months of tretinoin produced an eighty percent increase against a fourteen percent decline on vehicle alone. A four-year study found continued structural improvement.

Vitamin C, in the morning, if you buy it correctly, which means below pH 3.5 and between ten and twenty percent. Pinnell's original work found tissue levels saturating after three daily applications with a half-life of about four days, which is an argument for consistency rather than for quantity.

Something that supports the barrier, whenever your skin asks for it. The least glamorous item on the list and the one determining whether you can tolerate the other three.

That is the routine. Everything beyond it is optional, occasionally useful, and frequently the reason someone stops entirely.

The order, and why it matters less than you think

Morning: cleanse if you want to, vitamin C on clean skin, moisturiser if you need it, sun protection last.

Evening: cleanse, retinoid on dry skin, moisturiser after.

The one rule with real reasoning behind it is that vitamin C goes on clean skin, because its absorption depends on an acidic vehicle meeting the outer layer of skin directly. Sun protection goes last because it is a physical layer that other things should not be applied over.

Beyond those two, the ordering rules circulating online are mostly inherited from an era of harsher formulations, and they generate far more anxiety than they resolve. The genuine constraint is cumulative barrier disruption rather than any specific chemical incompatibility. A retinoid on the same night as a strong exfoliating acid is the combination most likely to leave you rebuilding for a fortnight; alternating nights resolves it.

Vitamin C and retinoids are often described as incompatible. Morning and night sidesteps the question entirely, and happens to suit both molecules for independent reasons.

Start smaller than feels reasonable

The most common failure in skincare is starting at full intensity and stopping within a month.

Begin the retinoid twice a week rather than nightly. The irritation that follows starting one is thoroughly documented, and the literature describes it as diminishing as treatment continues. But every study showing years of structural improvement was conducted on women who got through the onboarding phase. Someone who applies a retinoid nightly for three weeks, reacts badly and gives up has not tested the ingredient. She has tested her tolerance for a fortnight of flaking.

Increase frequency before increasing strength. Moving from twice to four times weekly at the same concentration is a larger real increase in exposure than jumping to a higher strength you use sporadically.

And moisturise alongside it. Barrier disruption is the mechanism of the irritation, so addressing it treats the problem itself rather than masking it.

What to leave out

Not because these things are useless, but because the evidence is thinner and the risk of abandoning the whole routine is real.

Exfoliating acids, beyond occasional use, tend to compete with a retinoid for the same barrier budget. Layering multiple actives on the same night is where most reactive skin originates.

Collagen supplements, of which reviews acknowledge that the variability of doses, ages, durations and outcome measures does little to support the robustness of the reported results.

And anything promising to address volume loss, which is a structural change happening beneath the skin in fat compartments and bone that no topical treatment reaches. That is not a criticism of the product. It is a criticism of the claim.

When to do less

There is a moment, familiar to most women, when skin becomes reactive and the instinct is to treat it harder because something is evidently wrong.

That instinct produces a loop. A compromised barrier loses water faster and admits irritants more easily. You respond with more actives. The barrier deteriorates further.

Three situations call for simplifying rather than escalating. During periods of high stress, where cortisol has been shown to reduce production of the very proteins that build the barrier. Around menopause, when reduced hyaluronic acid in the dermis means hydration falls and resilience with it, and products fine for years begin to sting. And after any procedure involving controlled injury, where healing capacity is the constraint.

In each case: fewer actives, more barrier support, and a pause on anything aggressive until the skin can support it again.

Where this belongs

Under Renew, which is the only lever operating every single day.

In most clinic versions of the five-lever framework, daily skincare appears as an afterthought, framed as protecting the results of the real treatments. That inverts its actual contribution. Procedures happen a handful of times a year. This happens seven hundred and thirty times, and it is the one thing determining whether anything else holds.

It is also the lever with the worst feedback loop. Nothing visible happens in a week. The retinoid studies measured change at twenty-four weeks, twelve months and four years. The sun protection you applied this morning will produce an effect you can observe in approximately a decade.

Which is why the routine that wins is the boring one you can hold indefinitely, and why the most useful thing you can do alongside it is keep a record. Change at this pace is invisible in a mirror you look into every morning. It is perfectly visible in photographs taken months apart.

Do four things. Do them badly rather than not at all. Do them for years.

References

1. Griffiths CEM, Russman AN, Majmudar G, Singer RS, Hamilton TA, Voorhees JJ, "Restoration of Collagen Formation in Photodamaged Human Skin by Tretinoin (Retinoic Acid)," New England Journal of Medicine 329(8):530-535, 1993. PubMed. Source of the 56, 80 and 14 percent figures.
2. Histologic evaluation of the long term effects of tretinoin on photodamaged skin00432-7/abstract), Journal of Dermatological Science, 1996.
3. Pinnell SR et al., "Topical L-Ascorbic Acid: Percutaneous Absorption Studies," Dermatologic Surgery 27(2):137-142, 2001.
4. Pujos M et al., "Impact of Chronic Moderate Psychological Stress on Skin Aging," Journal of Cosmetic Dermatology, 2024. Authors were employees of Coty Inc.
5. A Clinical Trial on Hydrolysed Collagen Supplementation, which itself notes the variability limiting the collagen supplement literature.