Tretinoin

Prescription-strength retinoic acid — the gold-standard topical for photoaging and acne, and the compound every cosmetic "anti-aging" routine is quietly benchmarked against. Decades of evidence, pennies per use, and still outperforms almost everything sold above it.

Tretinoin is vitamin A in its acid form, and unlike the retinol sold cosmetically it does not need converting — it binds retinoic acid receptors in the skin directly, which is why it is a prescription drug and retinol is not. Those receptors change which genes skin cells transcribe: cell turnover in the outer layer speeds up, the sticky plugs that form comedones loosen, and over months the deeper layer increases collagen production. That last effect is the one behind its anti-ageing reputation, and it is the slowest to arrive. The irritation everyone experiences in the first weeks is the same process — a genuinely accelerated turnover the skin has not adapted to yet.

As strong as topical dermatology gets: RCTs show improved fine wrinkles, texture and pigmentation over months, with histologic collagen increase. OTC retinol is a weaker prodrug of the same pathway — tretinoin is the evidence-bearing version.

• Extensively established for acne across decades of randomised trials, and a first-line treatment in dermatology guidelines worldwide.
• Photoageing evidence is also strong: randomised trials show measurable reductions in fine wrinkling, roughness and pigmentation over six to twelve months, with histological evidence of new collagen formation. This is one of very few topicals with that level of support.
• Effects are dose- and duration-dependent, and studies consistently show benefits continuing to accrue past the six-month mark rather than plateauing early.
• Comparative trials show cosmetic retinol is substantially weaker per unit than tretinoin, because of the conversion step — which is a real difference, not marketing.

Systemic absorption from topical use is low, and blood levels generally stay within the range produced by dietary vitamin A. That said, it is used at night because it is degraded by light, and it is applied to dry skin because application to damp skin increases penetration and irritation. Visible improvement in acne takes 8-12 weeks, and photoageing changes take six months to a year — the single most common reason people abandon it is expecting results on a cosmetic-product timescale.

The retinization period — weeks of dryness, peeling and irritation that makes most people quit exactly when it is starting to work. Photosensitivity (sunscreen becomes non-optional). Contraindicated in pregnancy. That is essentially the whole list, which is why it anchors this category.

• Anyone pregnant, breastfeeding or trying to conceive, without their clinician
• Anyone with eczema, rosacea or a compromised skin barrier, without dermatology input
• Anyone who will not use daily sun protection
• Anyone about to have waxing, laser or a chemical peel, until it has been paused appropriately

• Pregnancy — topical tretinoin is generally advised against in pregnancy, and oral retinoids are absolutely contraindicated. Anyone pregnant or trying to conceive should raise it with their clinician rather than assume topical means safe.
• Benzoyl peroxide, which oxidises and inactivates tretinoin if applied at the same time; separating them by time of day resolves it.
• Alpha and beta hydroxy acids, physical scrubs and alcohol-based toners, which compound irritation substantially.
• Waxing and laser treatment, where increased turnover raises the risk of skin lifting or injury; standard advice is to pause beforehand.
• Other vitamin A sources, which matters far more for the oral relatives of this drug than for topical use.

• The retinisation period — peeling, redness and stinging in the first two to six weeks. Expected, and it settles.
• The initial purge in acne use, where existing microcomedones surface. Distinguishing this from a genuine reaction usually comes down to whether spots appear where you normally break out.
• Sun sensitivity, which is real and requires daily sunscreen — not optional with this drug.
• Any severe or persistent burning, swelling or blistering, which is irritant contact dermatitis rather than normal retinisation.

No withdrawal effect and no rebound. Skin returns to its untreated behaviour over weeks to months: acne generally recurs if the underlying tendency is still there, and the collagen gained from long use is lost slowly rather than immediately. Stopping and restarting means going through the retinisation period again, which is the main practical argument for reducing frequency instead of quitting outright when it becomes irritating.

US: prescription-only topical; trivially available via dermatology telehealth.

Papers about this compound, not proof of the claims above. A title says what was studied, which is sometimes a negative result or a different question entirely.

• Comparing Tretinoin to Other Topical Therapies in the Treatment of Skin Photoaging: A Systematic Review
  Am J Clin Dermatol, 2024
• Topical tretinoin for treating photoaging: A systematic review of randomized controlled trials
  Int J Womens Dermatol, 2022
• Tretinoin Review With Newer Formulations: Providing Effective and Tolerable Solutions in Clinical Practice
  J Drugs Dermatol, 2023

• Comparing Tretinoin to Other Topical Therapies in the Treatment of Skin Photoaging: A Systematic ReviewAm J Clin Dermatol · 2024
• Topical tretinoin for treating photoaging: A systematic review of randomized controlled trialsInt J Womens Dermatol · 2022
• Tretinoin Review With Newer Formulations: Providing Effective and Tolerable Solutions in Clinical PracticeJ Drugs Dermatol · 2023
• Tretinoin peelingDermatol Surg · 2001
• Is tretinoin still a key agent for photoaging management?Mini Rev Med Chem · 2014
• Clindamycin/tretinoin: clindamycin phosphate/tretinoin gelDrugs R D · 2005
• Topical tretinoin research: an historical perspectiveJ Int Med Res · 1990
• Tretinoin tocoferil as a possible differentiation-inducing agent against myelomonocytic leukemiaLeuk Lymphoma · 1997
• Evaluating tretinoin formulations in the treatment of acneJ Drugs Dermatol · 2014
• Tretinoin therapy: practical aspects of evaluation and treatmentJ Int Med Res · 1990
• Topical tretinoin: its use in daily practice to reverse photoageingBr J Dermatol · 1990
• Tretinoin: a review of the nonclinical developmental toxicology experienceJ Am Acad Dermatol · 1997