What retinol does for the skin: how it works, what evidence it has and how soon it shows

Retinol improves the texture, the fine lines and the uneven tone of the skin, and it does so by changing the tissue, not just the surface: in the trial that demonstrates it best, collagen and the glycosaminoglycans of the dermis increased. Along with sunscreen, it is the cosmetic active with the best clinical backing.

It is also the one most exaggerated. This page separates the two: what has been measured — in whom, where and for how long — and what is claimed beyond that.

It is part of the guide to medical skincare, where the general framework of what a cosmetic can and cannot do is set out.

What it actually does to the skin

Retinol belongs to the family of retinoids, derivatives of vitamin A. All of them share one destination: to do anything, they have to end up converted into retinoic acid, which is the only form that binds to the cell’s nuclear receptors and changes which genes are expressed.

The chain has four links and runs in one direction only:

retinyl ester → retinol → retinaldehyde → retinoic acid

The further back in that chain a product starts, the gentler it is and the less active reaches the end. That is not a metaphor: in a classic study of skin metabolism, treating tissue with retinol or retinaldehyde produced detectable but small amounts of retinoic acid — of the order of 30 to 90 pmol — whereas applying retinoic acid directly left between 420 and 2,050 pmol depending on the compartment.

That bottleneck explains almost everything people notice with retinol: why it takes weeks, why it is better tolerated than a medicine and why raising the percentage does not multiply the effect the way it appears to.

When retinoic acid reaches the receptor, what follows is a real change in the activity of the skin: more cell turnover in the epidermis and, in the dermis, more synthesis of collagen and of ground substance.

What is proven, and in whom

First, the whole picture: what the systematic reviews say

Before looking at a single trial it is worth looking at the body of work, because that is where you see whether a result is a coincidence or a constant.

The whole family has consistent backing. A systematic review of randomised trials of topical tretinoin — the prescription retinoid, and the most studied of the family — started from 180 studies and kept seven randomised controlled trials, with concentrations from 0.025% to 5% and treatment lasting 3 to 24 months. Every one of them, without exception, reported improvement in the clinical appearance of photoageing — wrinkles, hyperpigmentation, dullness and lentigines — from the first month and sustained to 24 months.

And when it is compared with the alternatives, the important nuance appears. Another systematic review, this time of 25 comparative studies, set tretinoin against other topicals: the comparators were superior in 7 studies, equivalent in 13 and inferior in 3. In other words, in most comparisons they tie. And the authors add what really decides things in practice: most of those alternatives were less irritating and better tolerated, and they conclude that tretinoin remains the reference standard but that its poor tolerability limits its use.

🔑 Translated for anyone about to buy something: in this field the difference between products is usually smaller than the difference between using one and not using one. The most potent active, abandoned after three weeks, delivers nothing; a slightly gentler one kept up for six months delivers what the studies say.

The reference trial for retinol

The reference study was published in Archives of Dermatology in 2007. It is a randomised, double-blind, vehicle-controlled trial, with an elegant design: each participant received retinol on one arm and the vehicle on the other, so that each person was their own control.

What was done and what came out:

🔑 The important thing in the table is not the improvement: it is the last row. That there were changes in the collagen and in the ground substance of the dermis means that retinol changes the skin, it does not make it up. Very few cosmetic actives have a demonstration of that kind.

And what that study does not prove

It matters as much as the above, and it is almost never mentioned:

• It was not done on the face, but on the forearm, which is different skin and takes less accumulated sun in daily life.
• The population was very elderly — mean age 87 — which makes it hard to transfer the size of the effect to skin of 35.
• It was used at 0.4%, a concentration that is today above what the European Union permits in a facial cosmetic. That limit and what it implies are in the page on concentrations and the European limit.

Retinol against prescription retinoids

The question comes sooner or later: if retinoic acid is the one that acts, why not use it directly?

You can, but then we are no longer talking about a cosmetic. Tretinoin — retinoic acid — is in Spain a prescription-only medicine, and its AEMPS-authorised summary of product characteristics gives it two indications: mild to moderate acne vulgaris and, as adjunctive treatment, the reduction of fine lines, mottled hyperpigmentation and roughness of facial skin.

When the two have been compared on human skin, the result runs in the expected direction: four weeks of treatment with retinoic acid and with retinol both increased epidermal thickness and the expression of type 1 and 3 collagen genes, with retinol producing changes that were similar though smaller in magnitude.

Translated: retinol does the same thing, more slowly and more gently. Which one suits you is not a question of ambition but of indication, of tolerance and of whether there is a medical consultation behind it. It is a decision taken with a doctor, not in a corridor.

If retinol is not tolerated either: the alternative that does have a trial

It is the question that comes after two failed attempts, and it has an answer with data rather than marketing.

In a randomised, double-blind trial published in the British Journal of Dermatology, 44 patients used bakuchiol 0.5% twice a day or retinol 0.5% once a day for 12 weeks. The area of wrinkles and hyperpigmentation was measured with high-resolution photography.

The result has two parts and both matter:

• Both significantly reduced the area of wrinkles and of hyperpigmentation, with no statistical difference between them.
• Those using retinol reported more flaking and more facial stinging.

⚠️ With the usual caveats: it is 44 people and 12 weeks, not a meta-analysis. And the design itself does not compare quite like with like, because bakuchiol was applied twice a day and retinol once. It is a good signal, not a demonstrated equivalence.

🔑 Why it belongs on this page: it fits exactly what the review of 25 comparative studies says — alternatives of similar effectiveness and better tolerated — and it gives a real way out to anyone with reactive skin. Retinol being the standard does not make it the only option, and insisting on tolerating it when the skin says no usually ends in giving up altogether.

What retinol does not do

This is where a surgical clinic has something to say that an advert will not:

• 🚨 It does not tighten sagging tissue. A drooping eyelid, a facial oval that has lost its position or a neck with excess skin do not respond to a cosmetic, however good. The skin can be of better quality and still be where it is.
• It does not remove pigmentation on its own, although it helps. It improves uneven tone, but an established mark needs another strategy — it is in creams for facial pigmentation.
• It does not replace sun protection. On the contrary: it requires it. Without it, the night’s work is undone during the day.
• It does not treat acne the way a medicine does. It can accompany treatment, but acne is a diagnosis and has its own.
• It does not work faster by piling it on. Applying more, or more often, speeds up nothing; it irritates.

How long it really takes

The timescales the literature works with, worth having in mind before judging a product:

• Weeks 1 to 4. The adaptation phase. Dryness, tightness and flaking are to be expected. This is not the result, it is tolerance — and it is the point at which most people give up.
• Weeks 4 to 12. The first thing usually noticed: the skin looks smoother and more even. It is a change in texture.
• Week 12. The first honest point of measurement. The trials of niacinamide and other actives measure here.
• Week 24. Where the retinol trial measured fine lines and changes in the tissue. Six months.
• And beyond: up to 24 months. In the review of tretinoin trials, improvement was reported from the first month and maintained to two years of treatment. 🔑 It is the figure that most changes how to think about this: it is not a course that finishes, it is a habit that goes on paying.

⚠️ Any product promising a structural change in two weeks is promising something it cannot demonstrate, and the European Regulation on claims itself requires promises to be supported by evidence.

Who should consider it and who should not

It suits skin with signs of photoageing — uneven texture, fine lines, dull tone, visible pores — in someone prepared to keep it up for months and to use sun protection daily.

It is worth asking first if there is rosacea, atopic or seborrhoeic dermatitis, or a skin barrier already damaged by too many actives: in those cases retinol usually makes things worse before anyone is doing anything wrong.

🚨 And there are two situations in which you do not start without discussing it:

• Pregnancy and breastfeeding. Retinoids are the family treated with most caution. Tretinoin is contraindicated in pregnancy according to its summary of product characteristics, and with cosmetic retinol the usual advice is to stop. We go into it in how to start using retinol.
• Before surgery or a laser treatment. You need to know how far in advance to stop: it is in caring for your skin before and after surgery.

Frequently asked questions

Does retinol thin the skin?

No. It is a very widespread idea and the evidence runs in exactly the opposite direction: in the direct comparison between retinol and retinoic acid on human skin, both increased the thickness of the epidermis. The confusion comes from the flaking of the first few weeks, which makes the skin feel thinner when in fact it is turning over faster.

Can it be used in summer?

Yes, with daily sun protection — which is in fact the condition all year round. What is true is that retinol makes the skin more sensitive to radiation, and that the summary of product characteristics for tretinoin expressly recommends avoiding or reducing sun exposure during treatment and using a sunscreen. Many people prefer to lower the frequency in months of heavy exposure, and that is reasonable.

At what age should you start?

There is no established age, and be sceptical of anyone who gives a figure. What there is, is an indication: when signs of photoageing appear that bother you. On young skin without those signs, the expense and the irritation do not buy much; daily sun protection, by contrast, works from day one.

Are retinol and retinoic acid the same thing?

No, and it is the most common confusion. Retinoic acid — tretinoin — is the molecule that acts and in Spain it is a prescription medicine. Retinol is its precursor: the skin has to convert it in two steps, and most of it is lost along the way. They do similar things with different potency.

Can I use retinol if I have sensitive skin?

Often yes, but with a different approach: a low concentration, low frequency and repairing the barrier first. If the skin is constantly reactive, red and tight, the first step is not choosing a retinol: it is finding out why it is like that.

And if I stop using it, do I lose what I have gained?

The changes in the tissue do not disappear overnight, but retinol is not a treatment you are discharged from: it holds its effect while you use it. What does come back quickly when you stop is the previous texture. It is more useful to think of it as a sustainable habit than as a course.

Does bakuchiol work, or is it marketing?

It has a randomised, double-blind trial behind it, published in the British Journal of Dermatology: 44 patients, 12 weeks, bakuchiol 0.5% against retinol 0.5%. Both reduced the area of wrinkles and hyperpigmentation with no statistical difference between them, and those who used retinol reported more flaking and stinging. It is a good signal with its limits — a small sample and only 12 weeks — but it is not an ingredient without data: it is a reasonable option if retinol is not tolerated.

So which is the best product?

The question delivers less than it seems. In the review of 25 comparative studies, the alternatives to tretinoin tied with it in 13 of 25 comparisons and were generally better tolerated. In this field the difference between two good products is smaller than the difference between using one for six months and dropping it after three weeks. Choosing the one your skin can take is a more effective decision than choosing the most potent.

Can I combine it with vitamin C?

You can, and the usual approach is to separate them by time of day: vitamin C in the morning, retinol at night. The practical reason is not that they cancel each other out, but that both are demanding and together they increase irritation. The full order is in the order products go on.

Sources

• Kafi R, Kwak HS, Schumacher WE, Cho S, Hanft VN, Hamilton TA, King AL, Neal JD, Varani J, Fisher GJ, Voorhees JJ, Kang S. Improvement of naturally aged skin with vitamin A (retinol). Archives of Dermatology, 2007;143(5). PMID 17515510. — Randomised, double-blind, vehicle-controlled trial comparing right and left arms. Retinol 0.4% up to three times a week for 24 weeks in 36 elderly subjects (mean age 87). Significant improvement in fine lines (−1.64; 95% CI −2.06 to −1.22, against −0.08 for the vehicle) and a significant increase in glycosaminoglycans (p = 0.02) and in procollagen I immunostaining (p = 0.049).
• Sitohang IBS, Makes WI, Sandora N, Suryanegara J. Topical tretinoin for treating photoaging: A systematic review of randomized controlled trials. International Journal of Women’s Dermatology, 2022. PMID 35620028. — Of 180 studies examined, 7 randomised controlled trials were included, with tretinoin from 0.025% to 5% and treatment lasting 3 to 24 months. All consistently reported improvement in the clinical appearance of photoageing — wrinkles, hyperpigmentation, dullness and lentigines — from the first month and sustained to 24 months. The authors consider it safe and effective in the long term and call for more comparative research. ⚠️ Four of the studies included only women and the rest had mostly female participation.
• Siddiqui Z, Zufall A, Nash M, et al. Comparing Tretinoin to Other Topical Therapies in the Treatment of Skin Photoaging: A Systematic Review. American Journal of Clinical Dermatology, 2024. PMID 39348007. — PRISMA systematic review with a search up to December 2023: 25 comparative studies. Against tretinoin, the comparators were superior in 7 studies, equivalent in 13 and inferior in 3, and most were less irritating and better tolerated. Conclusion: tretinoin remains the reference standard, but its poor tolerability limits its use.
• Dhaliwal S, Rybak I, Ellis SR, et al. Prospective, randomized, double-blind assessment of topical bakuchiol and retinol for facial photoageing. British Journal of Dermatology, 2019;180(2):289-296. PMID 29947134. — Randomised, double-blind trial in 44 patients over 12 weeks: bakuchiol 0.5% twice a day against retinol 0.5% once a day. Both significantly reduced the area of wrinkles and hyperpigmentation, with no statistical difference between them; retinol users reported more flaking and facial stinging. ⚠️ A small sample, 12 weeks and different application frequencies in the two arms: it supports a signal, not an equivalence.
• Kong R, Cui Y, Fisher GJ, Wang X, Chen Y, Schneider LM, Majmudar G. A comparative study of the effects of retinol and retinoic acid on histological, molecular, and clinical properties of human skin. Journal of Cosmetic Dermatology, 2016;15(1). PMID 26578346. — Four weeks of treatment with retinoic acid and with retinol increased epidermal thickness and raised the expression of type 1 and 3 collagen genes; retinol induced changes similar to those of retinoic acid, tending to be smaller in magnitude.
• Bailly J, Crettaz M, Schifflers MH, Marty JP. In vitro metabolism by human skin and fibroblasts of retinol, retinal and retinoic acid. Experimental Dermatology, 1998;7(1). PMID 9517919. — After treatment with retinol and retinaldehyde, low but significant amounts of retinoic acid were detected in the epidermis and dermis (30–90 pmol), against much higher levels when retinoic acid was applied directly (2,050 and 420 pmol respectively). ⚠️ This is an in vitro study on human skin and fibroblasts: it supports the order of magnitude of the conversion, not an equivalence of clinical dose.
• AEMPS — CIMA. Summary of product characteristics for Retirides 0.5 mg/g cream (tretinoin). cima.aemps.es. — A prescription-only medicine. Authorised indications: mild to moderate acne vulgaris and adjunctive topical treatment for the reduction of fine lines, mottled hyperpigmentation and roughness of facial skin. Contraindicated in pregnancy. Recommends avoiding or reducing sun exposure and using sun protection during treatment.
• Commission Regulation (EU) No 655/2013 of 10 July 2013 laying down common criteria for the justification of claims used in relation to cosmetic products. Text in the BOE. — The “evidential support” criterion: claims must be supported by adequate and verifiable evidence, based on valid, reliable and reproducible methodologies.

Book your consultation

If you have been using a retinol for months and do not know whether it is doing anything — or if you have given up three times because it irritated you — it is worth reviewing in consultation: which concentration is right for you, how often, and whether the problem you want to solve is really one that responds to a cosmetic.

Clinical confirmation by the surgeon

Dr Enrique Salmerón González

Specialist in Plastic, Aesthetic and Reconstructive Surgery
Registration no. 46/4624077

Dr Elena García Vilariño

Specialist in Plastic, Aesthetic and Reconstructive Surgery
Registration no. 46/4624503

Last reviewed: 17 September 2026. This content is for information only and does not replace an individual assessment by a healthcare professional.