Tretinoin explained.

Tretinoin is a prescription-only topical retinoid — and the ingredient with the most robust body of evidence in skincare. It has been in clinical use for over fifty years. The evidence for its effects on acne, textural irregularity, fine lines, and photoageing is extensive. Understanding what tretinoin actually is, how it works at the cellular level, and how to introduce it correctly is the foundation for using it well.

What tretinoin is

Tretinoin is all-trans retinoic acid — the biologically active form of vitamin A. It is not a precursor. When you apply tretinoin, it does not need to be converted by the skin's enzymes before exerting its effects; it binds directly to retinoic acid receptors (RARs) in skin cells. This is what distinguishes tretinoin from over-the-counter retinoids such as retinol or retinaldehyde, which require one or two enzymatic conversion steps before becoming retinoic acid and reaching RAR binding. Each conversion step reduces potency. Tretinoin has no intermediate steps.

What it does

Accelerates cell turnover. Tretinoin binds to RARs in keratinocytes and upregulates gene expression associated with differentiation and shedding. The result is a faster transit of cells from the basal layer to the surface — typically measured in days rather than weeks. Faster turnover reduces the accumulation of dead cells inside follicles (a primary driver of comedonal acne), fades surface discolouration more quickly, and produces a more even skin texture over time.

Stimulates collagen synthesis. Tretinoin activates fibroblasts in the dermis and increases the expression of procollagen types I and III. It also inhibits matrix metalloproteinases — the enzymes that degrade existing collagen under UV exposure. The result over months of consistent use is denser dermal collagen, reduced fine line depth, and improved skin elasticity. This is the mechanism behind its evidence in photoageing.

Thins the stratum corneum, thickens the dermis. Counter-intuitively, tretinoin thins the outermost layer of the epidermis (the stratum corneum) through accelerated shedding, while increasing the thickness of the viable epidermis and dermis below. The net effect is skin that appears smoother and more refined at the surface with improved structural integrity underneath.

The evidence base

The evidence for tretinoin is extensive and covers multiple conditions. For acne, peer-reviewed studies spanning four decades demonstrate reductions in both comedonal and inflammatory lesions. For photoageing — fine lines, textural irregularity, solar lentigines — randomised controlled trials have shown measurable improvements with concentrations as low as 0.025% used consistently for six months or longer. For hyperpigmentation, tretinoin increases the rate at which melanin is dispersed through accelerated cell turnover, producing visible fading of post-inflammatory marks and melasma over time, particularly when combined with a daily SPF.

These effects are dose-dependent and time-dependent. Lower concentrations produce slower results with less irritation; higher concentrations produce faster results with greater adaptation demands. Consistent, long-term use is what produces the evidence-supported outcomes — not higher concentrations applied infrequently.

How to introduce tretinoin

Tretinoin causes an adaptation phase for almost everyone. The skin's initial response to accelerated cell turnover includes dryness, flaking, tightness, and temporary sensitivity. This is not damage — it is the expected physiological response to a significant change in cell turnover rate. Managing it correctly shortens the adaptation window and avoids barrier disruption that would slow progress.

Start low and infrequent. Begin with the lowest available concentration (typically 0.025% or 0.05%) applied two evenings per week. Hold at that frequency for four to six weeks before increasing to three evenings, then to every other evening, then to nightly if the skin is tolerating it well.

The buffer method. Apply moisturiser to damp skin, wait two to three minutes, then apply tretinoin. The moisturiser layer reduces the rate of absorption slightly and materially decreases initial irritation without meaningfully reducing efficacy over time. Once the skin has adapted — typically after two to three months — the buffer step is optional.

Apply to dry skin. Tretinoin applied immediately to wet skin absorbs more rapidly and causes greater irritation. Wait at least twenty minutes after washing before applying, or allow the skin to air-dry fully.

A pea-sized amount covers the whole face. More product does not produce better results; it increases irritation and wastes product.

What to avoid combining with tretinoin

Benzoyl peroxide — the combination increases oxidation and instability of tretinoin. Apply benzoyl peroxide in the morning and tretinoin in the evening if using both.

Other exfoliating actives on the same evening. AHAs, BHAs, and physical exfoliants applied on the same night as tretinoin compound the cell-shedding effect and tend to produce significant barrier disruption. Use them on alternating nights.

Vitamin C in the same step. L-ascorbic acid is most stable and effective at pH 2.5–3.5; tretinoin is most stable at a slightly higher pH. They work well as a morning/evening split — vitamin C in the morning, tretinoin in the evening.

Tretinoin versus OTC retinoids

Over-the-counter retinoids — retinol, retinaldehyde (retinal), granactive retinoid — require conversion to retinoic acid before exerting their effects. Each conversion step reduces efficacy. Well-formulated OTC retinoids are genuinely useful, and for many people they produce meaningful results without the adaptation demands of prescription tretinoin. The difference is one of directness and potency, not category — tretinoin is the benchmark; OTC retinoids approximate it at reduced strength.

For acne or significant photoageing concerns, tretinoin is the standard against which other retinoids are measured. It requires a prescription in Australia and most other markets — which means a consult with a GP or dermatologist, a barrier worth crossing for access to the most evidence-backed topical available.