Niacin for Skin Health
There is no good evidence that niacin (nicotinic acid) itself benefits skin health; the only meaningful skin data are for oral nicotinamide, a different form of vitamin B3, and even that benefit is weak, disputed, and limited to high-risk patients who have already had skin cancer.
Why this grade7-layer evidence engine
This claim earns only a weak (C) grade largely because of a form mix-up. The studied compound is oral nicotinamide, the non-flushing amide form of vitamin B3 - not niacin (nicotinic acid), the lipid-lowering acid form that mainly causes facial flushing and has no demonstrated skin benefit. Topical niacinamide cosmetic data (PMID 18492135) come from a separate delivery route and do not support taking niacin as an oral skin supplement.
Even for oral nicotinamide, the evidence is narrow and conflicting. The strongest study, the ONTRAC Phase 3 trial (PMID 26488693, n=386), cut new non-melanoma skin cancers by 23%, but only in immunocompetent people who had already had at least two skin cancers, and the benefit disappeared once the drug was stopped. The ONTRANS trial in transplant recipients (PMID 36856616) found no effect at all (rate ratio 1.0). A 2022 meta-analysis (PMID 35134311, n=3039) was positive (RR 0.50), but a stricter 2023 meta-analysis (PMID 38201930) found no significant effect (RR 0.82, 95% CI 0.61-1.12).
Regulators add caution rather than endorsement. The UK NHS and US FDA warn that high-dose nicotinic acid can cause skin flushing and, over time, liver damage, and the FDA withdrew its cardiovascular indications. The WHO recommends nicotinamide only to treat pellagra. For a healthy person seeking better skin, niacin supplements are not supported, and the chemoprevention dose is a medically supervised regimen for a specific high-risk group, not general consumer use.
Scoring transparency
All scores computed by a 7-layer evidence engine — fully auditable▸View the full decision path (audit trail)
- compute_raw_score — 加權公式: L2×0.30 + L3×0.25 + L5×0.25 + L11×0.10 + L1×0.10 = 0.697
- tier_from_score — 依分數區間映射至 tier letter
- apply_hec_rules — 高品質 SR/MA 顯示 positive (1 篇 > 0 negative)
- tier_strict_requirement_check — | B→C 因 scope.conflation_risk=true 且 L11 獨評較低 (B7-2 tier cap)
- detect_disputes — 偵測到 0 個 hard + 0 個 soft dispute
- decide_status — 依 tier + dispute 結果決定 status