Tretinoin: Why It Remains the Most Evidence Based Ingredient in Skincare, and What It Cannot Do

Last updated: 8 November 2026

In short: Tretinoin is the active form of vitamin A and the most studied topical ingredient in skincare, with biopsy evidence that it restores collagen formation and randomised trials showing improvement in fine lines, sun pigmentation and texture over months to years. It is a prescription only medicine in the UK, its use for sun damage and ageing is off label, and it is not for everyone: it irritates, it needs sun protection, and it must not be used in pregnancy. This article sets out what the evidence actually shows, what tretinoin cannot do, and how it fits with clinic treatments, so that a conversation with a prescriber starts from facts rather than hype.

If I could use one skincare ingredient for the rest of my life, it would be tretinoin, and I have said so in clinic in Hale more times than I can count. That is an opinion, and the skincare industry is full of opinions. What makes this one different is that tretinoin is the one topical ingredient whose claims have been tested the way medicines are tested: in randomised trials with placebo creams and in skin biopsies examined under a microscope, over more than forty years.

This article is the evidence, not the enthusiasm. It explains what tretinoin is and how it differs from the retinol you can buy, what the studies found and how strong they are, what it cannot do, who should not use it, why so many people give up in the first month, and how it fits alongside peels, microneedling and injectables. Tretinoin is a prescription only medicine. Nothing here is a recommendation to use it; whether it is right for you is a decision for a prescriber who has assessed your skin.

In this article:

• What is tretinoin, and how is it different from retinol?
• What the evidence actually shows, in order of strength
• What tretinoin cannot do
• How long does tretinoin take to work? The realistic timeline
• Side effects, who should not use it, and its prescription status in the UK
• Why most people give up in month one, and how not to
• Tretinoin and clinic treatments: what to pause and when
• Why I prescribe within a system, and my commercial interest
• What happens at my clinic in Hale
• Frequently asked questions

What is tretinoin, and how is it different from retinol?

Every vitamin A product that works on the skin works by becoming retinoic acid, the form skin cells can actually use. Tretinoin is retinoic acid. Everything sold over the counter is a step or more removed from it and has to be converted by enzymes in the skin, losing potency at each step.

Form of vitamin A	Steps to retinoic acid	Where it sits
Retinyl esters (retinyl palmitate)	Three	Very gentle, very weak; common in moisturisers that claim vitamin A
Retinol	Two	The standard over the counter retinoid; useful, well tolerated, with evidence of its own at higher strengths, and a sensible place to start
Retinaldehyde (retinal)	One	Stronger than retinol, still available without prescription; a good middle step
Tretinoin (retinoic acid)	None	Prescription only in the UK; the form the research was done on; the most effective and the most irritating
Adapalene and other synthetic retinoids	Act directly on the receptor	Prescribed for acne; less evidence for photoageing than tretinoin

The practical difference is not that retinol does nothing. It is that tretinoin is the molecule the trials used, at known concentrations, with measured results, and retinol is an approximation whose effect depends on how much of it your skin converts. For a fuller comparison see retinol vs prescription retinoids.

What the evidence actually shows, in order of strength

Claim	The evidence	How strong
It restores collagen formation	In a 1993 New England Journal of Medicine study, 29 people with sun damaged skin applied 0.1 per cent tretinoin or an identical cream without it for 10 to 12 months. On biopsy, new type I collagen formation rose by 80 per cent in the tretinoin treated skin and fell by 14 per cent in the vehicle treated skin	Strong: randomised, vehicle controlled, measured in tissue rather than by eye
It improves fine lines, sun pigmentation and texture	A 2022 systematic review found seven randomised controlled trials of tretinoin for photoageing, at concentrations from 0.025 per cent upwards and durations of 3 to 24 months, reporting improvement in wrinkling, mottled pigmentation, sallowness and sun spots, visible from about a month and sustained to two years	Strong for the direction of effect; the review notes the trials used different formulations and outcome measures
It is safe to use for years	The same review found every trial reported tretinoin as safe and well tolerated over its duration; the main problems were irritation and sun sensitivity, both manageable	Good, with the caveat that pregnancy is an absolute exclusion
It treats acne	Topical retinoids are a first line treatment for acne in UK and international guidance, and acne is tretinoin's licensed indication in the UK	Strong; this is medical treatment prescribed by your GP, not a cosmetic use
It keeps working for years	Trials extending to 24 months show continued, not plateaued, improvement; longer than that is clinical experience rather than trial data	Moderate; the two year data are good, the twenty year claims are extrapolation

"Topical tretinoin is a safe and effective therapeutic modality for long-term treatment of photoaging." 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.

The collagen finding is the one I come back to, because it is the thing almost every skincare product claims and almost none has shown. A cream that increases new collagen formation by 80 per cent on biopsy, against a placebo cream under which collagen formation fell, is not a marketing claim. It is a measurement. For why that matters in the wider picture of collagen loss, see why collagen declines and the treatments that actually stimulate it.

What tretinoin cannot do

The word "miracle" gets attached to tretinoin, including by me in a weaker moment, and it does the ingredient no favours, because it sets up the disappointment that makes people stop. Here is what it does not do.

It will not	Because	What does
Remove deep expression lines	A frown line is made by a muscle; thickening the skin over it softens the surface but does not stop the fold	Anti wrinkle injections following consultation, with tretinoin improving the skin that remains
Restore lost volume or lift	It works in the epidermis and upper dermis; flattened cheeks and jowls are fat and bone	Biostimulators such as Sculptra; surgery for marked skin excess
Clear melasma on its own	Hormonal pigment needs a pigment regulator alongside it; tretinoin alone helps, and alone can irritate pigment prone skin into more pigment	A prescription pigmentation programme following consultation
Work in six weeks	Six weeks is when the irritation settles; collagen remodelling takes months	Patience and photographs, below
Replace sunscreen	It makes skin more sun sensitive, and sun undoes the collagen it builds	Daily SPF, which in a randomised trial cut visible skin ageing by 24 per cent on its own
Suit everyone	Pregnancy, breastfeeding, eczema and rosacea prone skin, and some medicines rule it out or change the plan	An assessment, and sometimes retinol or nothing

How long does tretinoin take to work? The realistic timeline

Almost every tretinoin failure I see is a timing failure: the person stopped during the worst fortnight, or judged the result at the point where only the irritation had happened. This is the real calendar.

When	What is happening	What you see
Weeks 1 to 4	Cell turnover accelerates sharply; the barrier is disrupted while the skin adapts	Dryness, flaking, redness, stinging; often a crop of spots as blocked pores clear. This is the period people quit in, and it is temporary
Weeks 4 to 8	The skin adapts; irritation settles; the surface is already smoother	Brighter, smoother skin; makeup sits better; pores look smaller
Months 3 to 6	Pigment turnover and early dermal change	Sun spots and post spot marks fade; tone evens; fine lines start to soften
Months 6 to 12	New collagen accumulates in the upper dermis; this is where the 1993 biopsies were taken	Firmer, thicker feeling skin; fine lines visibly reduced; the change people notice in old photographs
Year two and beyond	Continued slow gain; maintenance at a tolerable frequency	The gap between your skin and your untreated contemporaries' widens year on year

Take a photograph in the same light before you start and every three months after. Memory is useless for slow change; photographs are not.

Side effects, who should not use it, and its prescription status in the UK

Issue	What you need to know	What it means in practice
Prescription only	In the UK tretinoin is a prescription only medicine. Its licensed use is acne; prescribing it for sun damage and ageing is off label, which is lawful and common but means the prescriber takes responsibility and must discuss it with you	It can only be supplied after a prescriber has assessed you face to face; anything sold without that is unlawful and possibly counterfeit
Pregnancy and breastfeeding	Retinoids as a class are associated with birth defects; topical absorption is low, but the rule is absolute: not in pregnancy, not when trying to conceive, not while breastfeeding	Stop before trying to conceive and tell your prescriber; retinol is also avoided
Irritation	Dryness, redness, flaking and stinging in the first month are expected, not an allergy; severe or persistent reaction is a reason to stop and be reassessed	Start low, go slow, buffer with moisturiser; see the next section
Sun sensitivity	Thinner stratum corneum and faster turnover make skin burn more easily	Daily SPF without exception; apply tretinoin at night
Eczema, rosacea, very reactive skin	A damaged barrier or an inflammatory condition can be made worse; the conditions themselves are for your GP	Barrier repair first, condition controlled first, then a cautious trial if appropriate, or retinol instead
Darker skin tones	Tretinoin works well and is widely used for pigmentation, but irritation can itself cause pigmentation in skin that pigments easily	Lower starting strength, slower build, strict SPF
Waxing, peels and other actives	Thinner surface skin lifts with wax and over reacts to acids and benzoyl peroxide used at the same time	No facial waxing; acids on alternate nights at most; pause before clinic treatments as below

Why most people give up in month one, and how not to

I wrote a whole article on this, the real reason your tretinoin is not working, because it is the single commonest conversation about tretinoin I have. The short version is below.

Mistake	What happens	Instead
Starting at full strength every night	A raw, peeling face by day ten and a tube in the bin by day fourteen	A pea sized amount two nights a week for a fortnight, then three, then alternate nights, then nightly if tolerated; months, not days
Applying to damp skin	Water increases penetration and irritation	Wait twenty minutes after cleansing; skin fully dry
Using it with acids, vitamin C and scrubs	The barrier cannot cope with everything at once	Tretinoin at night, vitamin C and SPF in the morning, acids rarely or not at all
Stopping when the skin purges	Blocked pores surfacing in weeks two to six are read as "it is giving me spots"	Expect it, keep going; a true worsening beyond eight weeks is a reason to be reassessed
Judging at six weeks	Only the irritation has happened yet	Judge at six months, with photographs
Skipping the moisturiser and SPF	The barrier never recovers and the sun undoes the collagen	Barrier moisturiser over the top at night, or sandwiched either side; SPF every morning

Tretinoin and clinic treatments: what to pause and when

Tretinoin and in clinic treatments work on the same collagen and reinforce each other, but a retinoid thinned surface reacts more to anything that disturbs it, so the timing matters.

Treatment	Tretinoin before and after	Why
Medical microneedling and microneedling with exosomes	Pause five days before and five days after	Open channels plus a retinoid means excessive irritation; the two together over a year build more collagen than either alone
Chemical peels	Priming with tretinoin for three to four weeks beforehand improves the result, then pause three to five days before and restart from around day ten to fourteen after a medium depth peel	Primed skin peels more evenly; freshly peeled skin cannot tolerate it
Polynucleotides and skin boosters	Pause the night before and for two or three nights after	Multiple small injection points heal faster without an active on top
Anti wrinkle injections, fillers, Sculptra, Radiesse	Continue; skip the night of treatment if the skin is tender	These work beneath the skin; tretinoin works in it; no conflict
Electrocautery	Pause until the treated spots have fully healed, usually ten to fourteen days	Healing crusts and a retinoid do not mix

Why I prescribe within a system, and my commercial interest

Tretinoin on its own fails for a predictable reason: nobody told the person how to get through the first six weeks. The clinics and brands that get good long term results all do the same unglamorous things around the prescription: a gentle cleanser, a barrier moisturiser, a schedule that builds slowly, SPF every morning, and someone to call when the skin flakes. The Obagi systems I use at the clinic are built that way, with tretinoin prescribed separately after consultation and the supporting products designed to carry it.

I should be plain about two things. First, the clinic is an Obagi stockist and I earn from selling the supporting products; that is a commercial interest and you should weigh my preference for one brand accordingly. Second, tretinoin is a prescription medicine and is not part of any product bundle: whether it is prescribed, at what strength and for what reason is a clinical decision made at a face to face consultation, and the same decision could equally be "not yet" or "retinol first". The system is the skincare around the prescription. The prescription is never a given. For how I decide between the strengths and formulations, see why I rate tretinoin so highly.

What happens at my clinic in Hale

Step	What happens
Consultation	Around 45 minutes with me, £75 redeemable against treatment or skincare. Skin type and concerns, medical history, medicines, pregnancy plans, previous retinoid use and how it went; your current routine reviewed product by product; photographs taken
The decision	Whether a prescription retinoid is appropriate at all, and if so which strength and formulation; for some people the answer is retinol first, barrier repair first, or a GP appointment first
The routine	Written out night by night for the first eight weeks: what to use, how often, how to buffer, and what is normal
Support	A direct line through the first six weeks for the flaking and the doubt, and a review at three months with photographs compared
Cost	Prescription tretinoin is priced separately from any skincare system, by strength, following consultation; current prices are on the price list

Patients come for skincare consultations from Hale, Altrincham, Bowdon, Hale Barns, Timperley, Sale, Wilmslow, Alderley Edge, Knutsford and Didsbury, and a good proportion of them have a half used tube of tretinoin in a drawer from a previous attempt. The tube was usually fine. The instructions were missing.

Takeaway: Tretinoin is the one skincare ingredient with biopsy proof that it rebuilds collagen and trial proof that it improves lines and sun damage over months to years. It is a prescription only medicine, off label for ageing in the UK, not for pregnancy, irritating at first and useless without sunscreen. Used slowly, with a barrier moisturiser and SPF, and judged at six months rather than six weeks, it does more for the skin than anything else in a bottle. Whether it is right for you is a prescriber's decision, not a blog's.

Frequently asked questions about tretinoin

Is tretinoin better than retinol?

It is stronger and better evidenced. Tretinoin is retinoic acid itself, the form the skin uses and the form the trials tested; retinol has to be converted in two steps and delivers a fraction of the effect. Retinol is still a reasonable choice for sensitive skin, for people who cannot have a prescription, and as a first step before tretinoin.

Can you buy tretinoin over the counter in the UK?

No. It is a prescription only medicine, supplied after assessment by a prescriber. Products sold online without a prescription are unlawful and may be counterfeit or incorrectly stored. Retinol and retinaldehyde are available without prescription.

Is tretinoin licensed for anti ageing in the UK?

No. Its licensed indication is acne. Prescribing it for sun damage and ageing is off label, which is legal and common, but it means your prescriber should explain that the use is outside the licence and take responsibility for the decision.

How long does tretinoin take to work?

Smoother, brighter skin at six to eight weeks; pigmentation improving from three months; fine lines and firmness from six to twelve months, which is when the collagen studies took their biopsies. The first month is irritation, not results.

Does tretinoin make your skin worse before better?

Often. Dryness, flaking and redness in the first few weeks are expected, and many people get a crop of spots as blocked pores clear. This settles by week six to eight with a slow start and a barrier moisturiser. Worsening that continues past eight weeks is a reason to be reassessed.

Can I use tretinoin if I am pregnant or trying to conceive?

No. Retinoids are avoided in pregnancy, when trying to conceive and while breastfeeding. Stop and tell your prescriber. Retinol is avoided too.

Does tretinoin thin the skin?

It thins the dead outer layer, which is why skin flakes and is more sun sensitive at first, and it thickens the living epidermis and dermis beneath by increasing cell turnover and collagen. Long term, tretinoin treated skin is thicker, not thinner.

Can I use tretinoin with vitamin C, acids or hyaluronic acid?

Vitamin C in the morning and tretinoin at night is a good pairing. Hyaluronic acid and a barrier moisturiser alongside it are helpful. Exfoliating acids are best used rarely or not at all while establishing tretinoin, because the barrier cannot cope with both.

Do I have to use tretinoin forever?

The benefit continues for as long as you use it and slowly fades over months if you stop. Most people settle on a maintenance frequency, often two to four nights a week, that they can sustain indefinitely.

Should I stop tretinoin before microneedling or a peel?

Yes. Pause five days before and after microneedling. Before a peel, tretinoin priming for a few weeks improves the result, then pause three to five days before and restart around day ten to fourteen after. Injectables do not require a pause.

Next steps

If you want to know whether a prescription retinoid is right for your skin, or you have tried one before and given up, book a skincare consultation at the clinic in Hale. You will leave with an assessment, a written routine, and the decision, which may well be to start with something gentler.

Learn more about Dr Caroline Warden Clinic

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Learn more about other treatments offered

Further reading

• The Real Reason Your Tretinoin Is Not Working
• Retinol vs Prescription Retinoids: What Works
• Why I Rate Tretinoin So Highly
• Why Prescription Skincare Should Never Be Bought Online
• Why Collagen Declines and the Treatments That Actually Stimulate It
• Five Skincare Ingredients I Would Be Careful With
• Medical Grade Skincare and Skincare Consultations in Hale and Altrincham

Dr Caroline Warden (GMC 6157708) is an NHS GP with over 19 years of clinical experience, an independent prescriber, and holds a Level 7 postgraduate diploma in cosmetic injectables. She has practised aesthetic medicine since 2017 and is the sole practitioner at Dr Caroline Warden Skin & Aesthetic Clinic, which she runs with her sister Louise at 2 Crown Passages, Hale, Cheshire, WA15 9GN, serving patients from Hale, Altrincham, Bowdon, Hale Barns, Timperley, Sale, Alderley Edge, Wilmslow, Knutsford, Didsbury and across Cheshire and South Manchester. The clinic was named Best Doctor Led Aesthetic Clinic in Cheshire 2026 by GHP. The clinic is an authorised Obagi stockist and sells skincare products; this is a commercial interest and is declared here. Tretinoin is a prescription only medicine; it is discussed in this article for information and is not promoted. It is prescribed, where appropriate, only after a face to face consultation, and the decision may be not to prescribe. The clinic does not diagnose or treat medical conditions; acne, eczema, rosacea and melasma are assessed by your own GP. This article provides general educational information and does not replace an individual consultation.

References

1. Griffiths CEM, Russman AN, Majmudar G, Singer KH, Hamilton TA, Voorhees JJ. Restoration of collagen formation in photodamaged human skin by tretinoin (retinoic acid). New England Journal of Medicine 1993;329(8): pages 530 to 535. Read the study
2. 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;8(1):e003. Read the review
3. Fisher GJ, Varani J, Voorhees JJ. Looking older: fibroblast collapse and therapeutic implications. Archives of Dermatology 2008;144(5): pages 666 to 672. Read the abstract
4. Hughes MCB, Williams GM, Baker P, Green AC. Sunscreen and prevention of skin aging: a randomized trial. Annals of Internal Medicine 2013;158(11): pages 781 to 790. Read the abstract
5. Medicines and Healthcare products Regulatory Agency. The Blue Guide: advertising and promotion of medicines in the UK. Read the guidance
6. National Institute for Health and Care Excellence. Acne vulgaris: management. NICE guideline NG198. Read the guideline