> ## Documentation Index > Fetch the complete documentation index at: https://docs.hi-doctor.ai/llms.txt > Use this file to discover all available pages before exploring further. # Tretinoin — the reference topical retinoid > Tretinoin is retinoic acid itself. How it acts on keratinisation and collagen, which strength is patient-orderable, and the pregnancy rule that governs it. Tretinoin is all-trans retinoic acid — the biologically active form of vitamin A, rather than a precursor the skin has to convert. That is what separates it from cosmetic retinol, and it is why it is prescription-only, why it is effective, and why it is more irritating than anything sold over a counter. ## What it is Active ingredient: **tretinoin**. On the [anti-ageing](/library/conditions/skin-ageing) pathway three strengths exist on the formulary — 0.025%, 0.05% and 0.1% — but **only 0.05% is patient-orderable**. The 0.025% and 0.1% strengths are doctor-only: they are dispensed solely where the reviewing doctor specifically selects them for the case, and they cannot be requested directly. Tretinoin 0.025% also appears as a component of the compounded [melasma](/library/conditions/melasma) combination formula. In the EU it is marketed under brand names including Retirides. **Pregnancy.** Topical retinoids, tretinoin included, are not used in pregnancy or when trying to conceive, and use while breastfeeding is avoided. The pregnancy step in both the anti-ageing and the melasma questionnaire is a hard gate for this reason. Anyone who could become pregnant should expect the reviewing doctor to ask about contraception before a retinoid is issued, and that decision is theirs. ## How it works Tretinoin binds directly to retinoic acid receptors in the cell nucleus, which act as ligand-activated transcription factors. The downstream changes to gene expression produce several effects at once. It reduces the abnormal cohesion of follicular keratinocytes that forms the microcomedone, and increases epidermal cell turnover. This is the anti-acne action, and it is also what improves surface texture. It increases procollagen production in the papillary dermis and reduces the activity of the matrix metalloproteinases that break collagen down. This is the mechanism behind its effect on fine wrinkling, and it is the slowest of its effects to appear. Accelerated epidermal turnover redistributes and clears pigment more quickly, which is why it is used alongside a tyrosinase inhibitor in the melasma combination rather than on its own. Continued use is associated with a thicker, more compact epidermis and a more even granular layer — the opposite of the thinning seen in intrinsic ageing. ## Retinisation The first four to six weeks on a retinoid are the hardest, and they have a name. Retinisation is the adjustment phase: dryness, flaking, tightness, stinging, redness, and often an apparent worsening of texture or an increase in visible lesions. It is a predictable consequence of accelerating epidermal turnover in skin that is not used to it, and it settles as tolerance develops. It is also the point at which most people abandon the medicine, which is why knowing about it in advance matters more than almost any other piece of information on this page. The two things that most reliably reduce retinisation are applying to **completely dry** skin — damp skin increases penetration and irritation — and starting at a reduced frequency rather than nightly. Buffering with a bland moisturiser applied before or after is also widely used. The [application guide](/library/guides/how-to-apply-topicals) covers the practical detail; the schedule itself is set by the reviewing doctor. ## What has been reported | Reported effect | Character | | ----------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | Dryness, peeling and scaling | Very common; the defining feature of retinisation | | Burning, stinging and erythema | Very common early, settling with continued use | | Photosensitivity | Expected. Tretinoin increases ultraviolet reactivity, and daily broad-spectrum sun protection is part of the treatment, not an optional addition | | Initial worsening of acne | Common where tretinoin is used for acne — lesions already forming below the surface mature faster | | Transient hyper- or hypopigmentation | Reported, and more relevant in darker phototypes where irritation itself can produce pigment | | Contact dermatitis | Uncommon; a spreading, intensely itchy or blistering reaction is a reason to stop and seek advice | | Tretinoin is degraded by light and by oxidisers | A formulation property rather than a side effect, and the reason it is conventionally applied at night and not layered with benzoyl peroxide in the same application | ## Realistic timelines Irritation, dryness and flaking. No visible benefit yet. Managed with reduced frequency and moisturiser. Irritation settles. Surface texture and smoothness are usually the first improvements to appear. Tone evens out and pigmentation typically begins to lighten. A baseline photograph in consistent lighting is the only honest comparison at this pace. Collagen-mediated improvement in fine wrinkling is the slowest change and continues with sustained use. Benefit regresses if treatment stops. ## Who it is not suitable for Anyone pregnant, trying to conceive or breastfeeding. Anyone with known hypersensitivity to tretinoin or an excipient. It is not applied to eczematous, broken or sunburnt skin, and it is not used alongside procedures or products that are already compromising the barrier. A history of poor tolerance to a retinoid is relevant information for the reviewing doctor rather than an automatic exclusion. Tretinoin also appears in some compounded scalp formulations used in [androgenetic alopecia](/library/conditions/androgenetic-alopecia), where it is included to increase the penetration of other actives rather than for its own effect on the hair follicle. ## How Hi-Doctor handles it The review is fully asynchronous — no video call, no telephone consultation. You complete the anti-ageing questionnaire, upload photographs if you choose to, and a registered doctor reviews the case and decides whether a retinoid is appropriate and at what strength. A prescription is never guaranteed; if one is not issued, the consultation fee is refunded in full. The medicine is dispensed and paid for at a pharmacy of your choosing — the [pricing page](/essentials/pricing) covers what the consultation fee includes. ## Related reading * [Skin ageing](/library/conditions/skin-ageing) · [melasma](/library/conditions/melasma) · [acne](/library/conditions/acne) * [Adapalene](/library/medicines/adapalene) — a more photostable retinoid, used on the acne pathway * [Hydroquinone](/library/medicines/hydroquinone) · [niacinamide](/library/medicines/niacinamide) * [How to apply a prescription topical](/library/guides/how-to-apply-topicals) * [Side effects of dermatology topicals](/library/guides/side-effects-dermatology) * [Safety and eligibility](/essentials/safety) ## Start a consultation Answer the anti-ageing questionnaire and a registered doctor reviews it. They decide whether a topical retinoid is appropriate and at what strength — and declining is a normal outcome. See [what it costs](/essentials/pricing) and [how the review works](/essentials/how-it-works). This page is reference information, not medical advice and not a prescription. Whether a medicine is appropriate for you is decided by a registered doctor after reviewing your consultation.