Topical retinol, a vitamin A cream or serum sold without a prescription in most countries, is used to slow visible skin aging. Evidence points to a real but modest smoothing of fine lines; gains in rough texture and firmness rest on thinner evidence, and any effect on uneven skin tone is uncertain. Irritation is the main cost. Evidence is moderate in quality and shaped substantially by industry funding. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Pregnancy test (hCG) | Negative; serum hCG below 5 mIU/mL in non-pregnant adults | Safety check: a positive result stops use |
| Photodamage grade (photonumeric scale) | No established target; track change from own baseline | Grade falls as fine wrinkling improves |
Cadence: Baseline standardized facial photographs and photodamage grade; repeated at 4 weeks, 12 weeks, then every 6–12 months. Irritation noted daily during the first 4–8 weeks of gradual build-up. For anyone who could become pregnant, a baseline pregnancy test as common precautionary practice, repeated whenever pregnancy becomes possible. No blood tests are needed for retinol alone.