Skincare ingredients, followed back to the evidence

Every ingredient carries a level saying how far human studies have actually got. Trials that found nothing are recorded the same way.

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Skin concernsStart from a concern and follow it to the ingredients.5 IngredientsTopical ingredients, each with an evidence level.12 ProductsProducts containing them — examples, not recommendations.In preparation MedicinesThings that are not cosmetics in Korea. Ask a doctor or pharmacist.4 ProceduresProcedures done at a clinic. Not something you use at home.In preparation

Skin concerns

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AcneIngredients: 1 PigmentationIngredients: 6 WrinklesIngredients: 7 DrynessIngredients: 5 RednessIngredients: 4

Ingredients

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Strong evidenceUV filter

Sunscreen

An ingredient class — not a single line on an ingredient list

An Australian trial randomised 1,621 people and followed them 4.5 years. Squamous cell tumour incidence was 39% lower (1,115 vs 1,832 per 100,000); basal cell carcinoma showed no difference. This is one of the few entries on this site carrying strong evidence.

Moderate evidenceRetinoid⚠ In pregnancy Do not use

Retinol

In a vehicle-controlled trial, 0.4% retinol applied for 24 weeks moved the fine-wrinkle score by −1.64 against −0.08 for vehicle. Thirty-six people, and it was forearms, not faces. In pregnancy, guidance says do not use it.

Moderate evidenceAntioxidant

Niacinamide

In a 12-week split-face study of 50 people, 5% niacinamide reduced fine lines, yellowing, red blotchiness and pigmented spots. The control was not nothing but the same moisturiser, and the manufacturer paid for the trial.

Medicines

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Things that are not cosmetics in Korea. Ask a doctor or pharmacist.

Moderate evidencePrescription only

TretinoinA prescription medicine in Korea. In a 1991 trial of 251 people, 79% of those using 0.05% for 24 weeks improved against 48% on vehicle. But in a 29-person trial in 2022, active and vehicle both improved 30–40% and could not be told apart.

Strong evidenceOver the counter — ask the pharmacist

Benzoyl peroxideA network meta-analysis of 179 randomised trials and about 35,000 observations found that the most effective topical option for mild-to-moderate acne was a retinoid combined with benzoyl peroxide, reducing lesion counts by 26.16% more than placebo. In Korea, single-ingredient products are available over the counter.

Moderate evidencePrescription only

AdapaleneAll 12 products registered in Korea are prescription-only. In a 67-person split-face trial, adapalene 0.3% with benzoyl peroxide 2.5% reduced scar counts by 15.5% over 24 weeks while the vehicle side increased by 14.4%.

Moderate evidenceOver the counter — ask the pharmacist

Azelaic acidAll six products registered in Korea are over the counter. In a Cochrane review, azelaic acid beat placebo on participants' own assessments (three trials pooled, risk ratio 1.52), and a phase 3 trial of a 15% foam also beat vehicle. The review noted that most included studies were at high or unclear risk of bias.

How the levels are set here

Cosmetic trials typically run 20–40 participants for 4–12 weeks and are paid for by the manufacturer. That is why 'strong evidence' is rare on this site — sunscreen and prescription retinoids are most of it.

Strong evidence: Consistent across several randomised controlled trials in people, or a meta-analysis.
Moderate evidence: Human trials exist, but they are small or the results disagree.
Early research: Test-tube or animal work, or a small pilot study. Not a result from skin.
Ingredient data: A fact from an ingredient list or a regulatory document. Not an efficacy claim.
Not established: Widely claimed, but not confirmed in people.