What Is Tretinoin?
Tretinoin (all-trans retinoic acid) is the active acid form of Vitamin A and the most clinically studied topical retinoid available. Unlike retinol — which must be converted by skin enzymes to retinoic acid through a multi-step process — tretinoin is already in its bioactive form and binds directly to nuclear retinoic acid receptors (RARs) to regulate gene expression. This directness makes it significantly more potent than equivalent concentrations of retinol: estimates suggest tretinoin is approximately 20× more potent than retinol by weight. It is prescription-only in most countries.
Clinical Evidence
Tretinoin's evidence base is the most robust of any topical anti-ageing ingredient. Landmark studies from the 1980s–90s (Kligman, Voorhees) demonstrated measurable increases in dermal collagen, normalisation of epidermal architecture, reduction in fine lines and wrinkles, and improvement in photodamage-related pigmentation. Its efficacy for acne is equally established — it normalises follicular keratinisation, reducing comedone formation and bacterial proliferation. It is FDA-approved for both acne and photoageing treatment.
Concentrations and Forms
Available from 0.01% to 0.1%. Starting concentration is typically 0.025% cream (gentler than gel formulations). Effective range for photoageing: 0.025–0.05%. For acne: 0.05–0.1%. Cream vehicles are gentler; gel vehicles have faster penetration but more irritation. Encapsulated and slow-release formulations improve tolerability.
The benchmark: In dermatology, tretinoin is the reference standard against which all other anti-ageing ingredients are measured. If an ingredient claims to match tretinoin efficacy without prescription, that claim requires extraordinary evidence — which currently does not exist.
See Retinoids Guide and Retinization.