Tretinoin, a prescription form of vitamin A applied topically at night, is used to reverse visible sun damage. Many controlled trials show it softens fine wrinkles, smooths rough texture, and fades sun spots over months of steady use, less so on deeper wrinkles; it did not prevent skin cancer in a large trial. Early redness, peeling, and stinging usually settle. Overall, a modest, well-documented, low-cost improvement with a demanding routine. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Pregnancy test (urine or serum) | Negative | Excludes fetal exposure |
| Photodamage severity score (Griffiths 0–9 scale) | No universal target; at least 1-point improvement from own baseline by 6–12 months | Quantifies response |
| Standardized facial photography | No numeric target; compared against own baseline | Documents wrinkles and pigment objectively |
| Serum 25-hydroxyvitamin D | 40–60 ng/mL (100–150 nmol/L) | Detects deficiency from strict sun avoidance |
| Skin hydration and water loss through the skin | No established target; return to own pre-treatment values by 8–12 weeks | Gauges barrier recovery |
Cadence: Baseline before starting; skin tolerance check at 2–4 weeks; photographs and photodamage score at 3, 6, and 12 months, then every 6–12 months during maintenance; vitamin D yearly; pregnancy testing whenever pregnancy is possible