Retinol, retinal or tretinoin: strengths, conversion and results
They differ by how far they sit from retinoic acid, the only form a skin cell can read. Tretinoin is retinoic acid and needs no conversion, retinal is 1 enzymatic step away and retinol is 2, which is why a 2006 review puts retinol at 20 times less potent than tretinoin at the same concentration. Since Commission Regulation (EU) 2024/996, a cosmetic sold in the EU may carry at most 0.3 percent retinol equivalent in a face product and 0.05 percent in body lotion, so the strongest legal cosmetic sits below a 0.05 percent tretinoin prescription. Acne usually answers in 2 to 3 weeks, fine lines in 3 to 4 months, and dermal collagen needs more than 6 months.
The conversion chain behind every retinoid
Every retinoid is judged by one question. How far is it from retinoic acid, the only form the nuclear receptors in a skin cell can read? Tretinoin is retinoic acid, so it needs 0 conversions. Retinal, short for retinaldehyde, is 1 oxidation step away. Retinol needs 2 steps, first to retinal and then to retinoic acid. Retinyl esters such as palmitate, acetate and propionate sit behind retinol again, because the ester has to be cleaved before the chain can even start.
Each step costs potency. A 2006 review in Clinical Interventions in Aging, drawing on work from 1994 and 1995, puts retinol at 20 times less potent than tretinoin at the same concentration. That is why 0.3 percent retinol and 0.05 percent tretinoin are not comparable products, even though the retinol figure on the label is 6 times larger.
Conversion is also a bottleneck you cannot see on a carton. The same review notes that retinaldehyde is turned into retinoic acid only by keratinocytes at a particular stage of differentiation, which makes the delivery more controlled and the adverse effects weaker than with tretinoin. That governed step is the argument for retinal.
| Form | Steps to retinoic acid | Strengths in the studies cited | Where you get it | Irritation |
|---|---|---|---|---|
| Retinyl esters (palmitate, acetate, propionate) | 3 | 0.15 percent propionate over 48 weeks | Cosmetic, the cap names palmitate and acetate, not propionate | Lowest, and no advantage over placebo in that trial |
| Retinol | 2 | 0.3 percent and 1 percent over 6 weeks | Cosmetic, capped at 0.3 percent in EU face products | No or mild reaction in 88.7 percent at 0.3 percent |
| Retinal (retinaldehyde) | 1 | 0.05 percent over 4 months | Cosmetic, not named in the 2024 EU entry | Lower than equal strength retinoic acid |
| Tretinoin | 0 | 0.001 to 0.1 percent, followed up to 22 months | Prescription | Highest, with peeling and stinging common |
| Adapalene | 0, it is synthetic | 0.1 and 0.3 percent in the one ageing study | Prescription in the UK, over the counter in the US | Lower than tretinoin through receptor selectivity |
What the EU now allows in a cosmetic
Until 2024 there was no concentration limit on retinol in EU cosmetics. Commission Regulation (EU) 2024/996 of 3 April 2024 changed that, adding retinol, retinyl acetate and retinyl palmitate to Annex III of Regulation (EC) No 1223/2009 as entry 376. Two ceilings now apply: 0.05 percent retinol equivalent in body lotion, and 0.3 percent retinol equivalent in every other leave-on and rinse-off product, the face included.
The reasoning is not irritation. The Scientific Committee on Consumer Safety, which reported on vitamin A on 6 October 2016 and adopted a revised opinion on 24 and 25 October 2022, judged those levels safe on the skin but flagged total vitamin A intake. Around 5 percent of the population already sits at the top of the exposure range from food and supplements, so any product containing these ingredients must now carry the sentence Contains Vitamin A. Consider your daily intake before use.
Two dates decide what you can still buy. From 1 November 2025 a non-compliant product could no longer be placed on the EU market, and from 1 May 2027 it may not be made available at all. A 1 percent retinol cream that was legal in 2023 is not a legal EU face product now, so 0.3 percent is the working ceiling without a prescription.
Where a prescription changes the arithmetic
A prescription moves you past the conversion problem entirely. Topical tretinoin has been studied from 0.001 percent up to 0.1 percent, with 0.05 percent as the workhorse of the photoageing literature: a randomised double-blind trial in 30 patients over 6 months, a 533 patient dose comparison in which 0.05 percent beat both 0.01 and 0.001 percent, and elsewhere daily application followed for a full 12 months.
The NHS names tretinoin and adapalene as the topical retinoids used for acne in the UK, and the instruction is precise. Apply once a day before bed, to all affected parts of the face, 20 minutes after washing, and sparingly. A 6 week course is usually required, after which many people carry on less often to stop acne returning.
Adapalene is the chemical outlier. It is a third generation synthetic retinoid that binds the retinoic acid receptors selectively instead of being converted from anything, and that selectivity is why it irritates less than tretinoin does. Where you buy it depends on the country. In the UK it is a prescription medicine, while the US Food and Drug Administration moved a 0.1 percent adapalene gel to over the counter sale in 2016, for ages 12 and above. Its evidence in ageing is thin, resting on a single 2 centre randomised study in 83 patients with actinic keratoses and solar lentigines, run at 0.1 and 0.3 percent, against decades of tretinoin trials. Strength printed on a label and strength delivered to a cell are two different measurements.
| Goal | First few weeks | Sensible review point | Where the figure comes from |
|---|---|---|---|
| Acne | Often worse for 7 to 10 days | 2 to 3 weeks, sometimes past 6 | Drug information for topical tretinoin |
| A full acne course | Mild stinging and irritation | 6 weeks | NHS acne treatment guidance |
| Texture and roughness | Not assessed before month 4 | 4 months | Open trial of 0.05 percent retinaldehyde in 32 women |
| Fine lines | Little to see before month 3 | 3 to 4 months, up to 6 | Drug information for topical tretinoin |
| Dermal collagen | Nothing visible at 6 months | 12 months and beyond | Long term tretinoin studies in the 2006 review |
How long before anything shows
Acne and ageing run on different clocks. For acne, the drug information on topical tretinoin from the US National Library of Medicine warns that skin probably gets worse during the first 7 to 10 days, with redness, scaling and more spots, before improvement appears at 2 to 3 weeks and sometimes only after more than 6 weeks.
For lines and texture the figures are longer. The same drug information puts noticeable change in wrinkles at 3 to 4 months, and sometimes up to 6 months. Appreciable improvement at the dermal level takes more than 6 months of tretinoin, and in a 22 month study of 16 patients who began on 0.1 percent, wrinkle improvement kept rising until roughly the 10th month and then held.
That gap between the surface and the dermis explains most disappointment. Cell turnover answers in weeks, which you read as smoother and slightly pinker skin. Collagen answers in seasons. Judging a retinoid at week 8 means reading an early frame of a 12 month process, and before-and-after photographs taken in different light will tell you whatever you want to hear.
Concentration, tolerance and the ramp
Higher is not automatically better. A 2022 study in the International Journal of Cosmetic Science put 218 women aged 35 to 70 through 6 weeks of retinol at an escalating frequency, 115 of them on 0.3 percent and 103 on 1 percent. In the lower group 88.7 percent reported no reaction or only a mild one, against 62.1 percent at 1 percent, a difference that held statistically.
The same work measured what the bigger number buys. In a patch test on 5 volunteers aged 66 to 84, occluded for 12 days, epidermal thickness rose from 42.3 micrometres at baseline to 92.7 micrometres under 0.3 percent retinol and 122.3 micrometres under 1 percent. Those are biopsies under a patch, not a face washed every morning, and the work was funded by a cosmetics company whose staff are among the authors.
Esters mark the other end of the range. A double-blind, placebo-controlled trial in 60 people ran 0.15 percent retinyl propionate for 48 weeks and found no significant advantage over placebo on any sign of photoageing. Retinal sits at the opposite pole: in a randomised comparison of 125 volunteers, 0.05 percent retinaldehyde matched 0.05 percent retinoic acid on wrinkles and roughness, with fewer irritant reactions. An earlier open study of 32 women at 0.05 percent over 4 months reported less roughness and coarse wrinkling, but open studies without a control group are the weakest evidence here.
Who should not use one
Pregnancy is the hard line. The NHS states that topical retinoids are not suitable during pregnancy because of the risk of birth defects. If you are pregnant, trying to conceive or breastfeeding, stop and speak to a doctor or pharmacist before you start or restart, and the drug information for topical tretinoin asks the same, with a call to your doctor if you become pregnant while using it. Oral retinoids sit under stricter pregnancy prevention rules again and are never a cosmetic decision.
Set a retinoid aside during a flare of eczema or rosacea, on broken or sunburnt skin, and in any week you are also using strong acids or recovering from a peel. Retinoids raise sensitivity to sunlight and to sunlamps, so a sunscreen every morning belongs to the method rather than sitting beside it. In deeper skin tones the same irritation can leave a dark mark that outlasts the redness by months, which argues for a slower ramp rather than for a stronger product.
The retinoid reaction itself, meaning itching, burning, redness and peeling, is more pronounced with tretinoin and tazarotene than with retinol or retinal. Mild irritation and stinging are what the NHS lists as the most common side effects of a topical retinoid. Swelling, weeping skin or a spreading rash is not, and that is a call to a doctor.
A 12 week ramp most skin tolerates
- Weeks 1 and 2, apply a thin layer to dry skin on 2 nights a week, with no acids or scrubs on those nights.
- Weeks 3 to 6, move to every other night if there is no peeling, and wait 20 minutes after washing before you apply.
- Weeks 7 to 12, go nightly only if week 6 was calm; staying at 3 to 4 nights a week is a legitimate end point.
- Wear a sunscreen every morning, because retinoids raise sensitivity to sunlight and to sunlamps.
- Pause for 2 to 3 nights at the first stinging that is still there in the morning, then restart one step back.
- Judge acne at 6 to 12 weeks and lines at 6 months, in the same light and at the same time of day.
- Stop and speak to a doctor if you are pregnant, planning a pregnancy or breastfeeding.
Frequently asked
Is retinal stronger than retinol?
Retinal sits 1 enzymatic step from retinoic acid where retinol sits 2, so less conversion stands between the molecule you apply and the form the receptors read. In a randomised trial of 125 volunteers, 0.05 percent retinaldehyde matched 0.05 percent retinoic acid on wrinkles and roughness while causing fewer irritant reactions.
Why was retinol limited to 0.3 percent in the EU?
Commission Regulation (EU) 2024/996 capped vitamin A in cosmetics at 0.3 percent retinol equivalent for face products and 0.05 percent for body lotion, following the Scientific Committee on Consumer Safety. The concern was total vitamin A intake in the roughly 5 percent of people already at the top of the exposure range from food and supplements, not irritation on the skin.
Can I use a retinoid while pregnant or breastfeeding?
No. The NHS states that topical retinoids are not suitable during pregnancy because of the risk of birth defects, and the drug information for topical tretinoin asks you to tell your doctor if you are pregnant, planning a pregnancy or breastfeeding.
How long before I see anything?
Acne usually starts improving at 2 to 3 weeks and sometimes takes more than 6, with a 6 week course the usual plan. Fine lines take 3 to 4 months and sometimes up to 6, and new dermal collagen has only been shown after more than 6 months of tretinoin.
Is peeling in the first weeks normal?
Mild irritation and stinging are the most common side effects of topical retinoids, and with tretinoin for acne the skin often turns redder and scalier for the first 7 to 10 days. A spreading rash, swelling or weeping skin is not part of that and needs a doctor.
Does a higher percentage work better?
Not reliably. Among 218 women, 88.7 percent on 0.3 percent retinol reported no reaction or a mild one against 62.1 percent on 1 percent, and a 0.15 percent retinyl propionate cream tested in 60 people over 48 weeks showed no significant advantage over placebo.
Sources
- Commission Regulation (EU) 2024/996 of 3 April 2024 · The EU legal text adding retinol, retinyl acetate and retinyl palmitate to Annex III of Regulation (EC) No 1223/2009 as entry 376. Source of the 0.05 percent retinol equivalent limit for body lotion, the 0.3 percent limit for other leave-on and rinse-off products, the obligatory vitamin A labelling sentence, the SCCS opinion dates and the deadlines of 1 November 2025 and 1 May 2027.
- Retinoids in the treatment of skin aging, Clinical Interventions in Aging 2006 · Review hosted by the US National Library of Medicine. Source of the conversion pathway, the finding that retinol is 20 times less potent than tretinoin, the retinaldehyde studies in 32 and 125 volunteers, the 0.15 percent retinyl propionate trial in 60 people over 48 weeks, the tretinoin dose comparisons in 30 and 533 patients, the 22 month tretinoin study in 16 patients and the adapalene study in 83 patients.
- Multifaceted amelioration of cutaneous photoageing by 0.3 percent retinol, International Journal of Cosmetic Science 2022 · Tolerance study in 218 women aged 35 to 70 plus a 12 day patch test in 5 volunteers aged 66 to 84. Source of the tolerance figures of 88.7 percent and 62.1 percent and the epidermal thickness measurements of 42.3, 92.7 and 122.3 micrometres. The work was funded by a programme grant from a cosmetics company whose staff are among the authors, so it is read here as industry evidence.
- Acne treatment, NHS · United Kingdom health service guidance. Source of the 6 week course, the instruction to apply once a day before bed and 20 minutes after washing, the naming of tretinoin and adapalene, the usual side effects and the statement that topical retinoids are not suitable during pregnancy because of the risk of birth defects.
- Tretinoin topical, MedlinePlus drug information · US National Library of Medicine drug information. Source of the 7 to 10 days of worsening, improvement at 2 to 3 weeks and sometimes after more than 6, the 3 to 4 month and up to 6 month window for wrinkles, the sunlight and sunlamp warning and the pregnancy and breastfeeding advice.
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This guide is for general information. It does not replace advice from a dermatologist, physician or qualified practitioner, or an examination.