How do we read skin evidence — where the endpoints are cosmetic, the funding is industry, and the RCT is nearly impossible?
Skin research has a measurement problem, a funding problem, and an ethics limit that shape everything this page can honestly claim: the endpoints are often surrogates (hydration readings, elasticity scores) rather than outcomes (cancer incidence, disease control); the beauty literature is predominantly industry-funded (the disclosure-reading skill this chapter teaches); and no ethics board will ever randomize people to sunburn — which is why the Nambour sunscreen trial stands alone as the field's only prevention RCT, and why its melanoma result carries the weight it does. We interpret the literature in the context of AAD guidelines.
The field teaches endpoint, funding, and population literacy like no other:
Robert Willan's illustrated classification of skin diseases gives the surface its own medical specialty — built on the observation that skin reads the inside.
Niels Felsen Finsen concentrates UV light to treat cutaneous tuberculosis (lupus vulgaris) — phototherapy born, Nobel-honored in 1903: the first therapeutic use of the radiation that also damages.
The photosensitive dermatitis of pellagra traced to niacin deficiency — nutrition announced on skin before any lab could measure it, and the disease that killed 100,000+ Americans was ended by diet.
The vitamin D pathway is elucidated — the skin-UVB-cholesterol reaction identified as the hormone's factory floor. The organ's endocrine role enters the textbooks.
Topical tretinoin approved for acne (1971); the 1988 photoaging trials prove it improves sun-damaged skin — the first and still the only proven anti-aging topical, and prescription-only to this day.
1,621 Queensland adults randomized to daily versus discretionary sunscreen — the trial that would prove, at its 10-year follow-up, that daily SPF roughly halves invasive melanoma.
Anti-IL-17/IL-23 biologics clear psoriasis visibly; AI-assisted dermoscopy and teledermatology extend the diagnostic eye — the specialty advancing at both its poles: the molecular and the visual.
POPULATION · 1,621 Queensland adults randomized to daily vs. discretionary sunscreen, 4.5-year intervention, decade of follow-up
FINDING · Daily sunscreen use roughly halved invasive melanoma incidence versus discretionary application at long-term follow-up — the only RCT of sunscreen and skin cancer ever conducted.
LIMITATION · Single high-UV region; the control arm used discretionary sunscreen, not none; one trial carries an entire prevention field — and remains the most decisive data point skin prevention has.
POPULATION · Young men with acne, low-glycemic-load versus control diet, 12 weeks
FINDING · The low-glycemic diet reduced acne lesion counts and improved insulin sensitivity versus control.
LIMITATION · Small sample; weight loss in the intervention arm is a confounder; single-research-group replication — directionally consistent across the series, but the effect is not the prescription tier's.
POPULATION · Identical twin pairs discordant for long-term smoking, standardized facial photography, blinded scoring
FINDING · The smoking twin consistently showed greater facial wrinkling, sagging, and apparent age — decades of smoking written on the surface, with genetics held constant.
LIMITATION · Observational — but twin-controlled (the genetic variable equalized), with effect sizes consistent with elastosis and microvascular mechanisms: the most visually persuasive aging evidence the field has.