Retinol and retinoids: what is actually proven

If there is one ingredient on which dermatology and the cosmetics industry broadly agree, this is it. Retinoids are the best-studied class of compounds against photoageing — and simultaneously the one most frequently misrepresented in advertising. This article sets out what is established, what is not, and how the over-the-counter form differs from the prescription one.

What retinoids actually are

Retinoids are a group of compounds chemically derived from vitamin A. Four forms matter for the skin, and they differ considerably in potency:

• Retinyl esters (e.g. retinyl palmitate) — the weakest form, common in inexpensive cosmetic products
• Retinol — available over the counter; the most widely used effective form in cosmetics
• Retinaldehyde — an intermediate step, more potent than retinol, also available over the counter
• Tretinoin (retinoic acid) — prescription-only in Germany; the most potent and best-supported form

The decisive point: in the skin, every precursor must first be converted into the active form. Each conversion step costs potency. Retinol has to be converted twice before it acts as tretinoin — so at an equal concentration, retinol delivers only a fraction of tretinoin's strength.

How they work

Retinoids bind to specific receptors in the cell nucleus and thereby change which genes are read. Several effects follow at once:

• Cell renewal in the epidermis is stimulated and the horny layer becomes more even
• Collagen production in the dermis increases while its breakdown is slowed
• Pigment distribution becomes more even and sun spots fade
• Abnormal keratinisation in the sebaceous duct improves — which is why retinoids are also used for acne

The timescale matters. A visible change in the skin takes months, not weeks. Studies typically measure at twelve to twenty-four weeks — and even then the effects are clear but not dramatic.

What the studies show

The evidence for tretinoin is unusually strong for a topic from the beauty sector. Controlled trials published as early as the mid-1980s showed improvements in fine lines, skin roughness and pigmentation under tretinoin [1][2]. Later reviews confirmed these findings and added histological evidence: under tretinoin, an actual increase in dermal collagen can be demonstrated — not merely an optical effect [3].

For over-the-counter retinol the evidence is weaker but real. Studies point in the same direction, with smaller effect sizes and greater variation between products [4]. Part of the reason is that retinol is sensitive to light and prone to oxidation: a product in a clear jar may have lost a substantial share of its potency by the time it is used up.

Retinoids are the only skincare ingredient for which a structural change in the skin — rather than merely a surface effect — has been convincingly demonstrated.

Retinol or tretinoin?

For many people retinol is a sensible starting point — not because it is better, but because it is accessible and better tolerated. Anyone with pronounced sun damage, or who sees no change after several months on retinol, should discuss the matter with a physician.

Use, side effects and the most common mistake

The typical side effects are well known and almost the rule in the first few weeks: dryness, flaking, tightness, redness, and occasionally a temporary flare of blemishes. They are unpleasant but as a rule harmless and self-limiting.

The most common mistake is starting too fast. Applying a high concentration daily from the outset provokes irritation, leads to stopping — and to the conclusion that the product is unsuitable. Building up slowly over several weeks is considerably more likely to succeed.

Equally important: retinoids increase the skin's sensitivity to light. Without consistent sun protection you work against your own ingredient, because UV radiation is precisely the factor whose consequences the retinoid is meant to improve [5].

Who should not use retinoids

• Pregnancy and breastfeeding: retinoids are not to be used during this time. For oral retinoids the teratogenic effect is clearly established; for topical use, avoidance is advised as a precaution.
• Active skin conditions such as marked eczema or a rosacea flare — medical assessment is needed here.
• Concurrent irritating treatments such as peels or ablative laser procedures — coordination with the treating practitioner is required.

Assessment

Retinoids are among the few skincare ingredients where the effort can be justified by evidence. They do not, however, replace sun protection — they complement it. If only one of the two is feasible, choose sun protection: it prevents damage, whereas a retinoid only partially improves damage already present.

A realistic expectation belongs with this: retinoids improve skin texture, fine lines and pigmentation. They do not replace an aesthetic treatment and will not remove deep folds or volume loss.

References

1. Kligman AM, Grove GL, Hirose R, Leyden JJ. Topical tretinoin for photoaged skin. Journal of the American Academy of Dermatology, 1986.
2. Weiss JS, Ellis CN, Headington JT, Tincoff T, Hamilton TA, Voorhees JJ. Topical tretinoin improves photoaged skin. A double-blind vehicle-controlled study. JAMA, 1988.
3. Mukherjee S, Date A, Patravale V, Korting HC, Roeder A, Weindl G. Retinoids in the treatment of skin aging: an overview of clinical efficacy and safety. Clinical Interventions in Aging, 2006.
4. Zasada M, Budzisz E. Retinoids: active molecules influencing skin structure formation in cosmetic and dermatological treatments. Postępy Dermatologii i Alergologii, 2019.
5. Hughes MC, Williams GM, Baker P, Green AC. Sunscreen and prevention of skin aging: a randomized trial. Annals of Internal Medicine, 2013.

Last reviewed: August 2026. This article will be revised as soon as the evidence changes materially.