Ingredients

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.

Evidence level

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.

Ingredient dataRetinoid

Retinyl palmitate

Retinyl Palmitate

It is one of four actives notified for wrinkle claims in Korea, and at 10,000 IU/g a product may carry that claim without submitting efficacy data of its own. But we found no human trial that measured this ingredient alone. Both trials we opened are mixtures — one blends it with retinol and retinyl acetate, the other puts it in an oil with antioxidants.

Early researchSoothing

Licochalcone A

In an 80-person randomised, investigator-blinded trial, a moisturiser containing licochalcone A was compared against 0.02% triamcinolone acetonide cream. The steroid improved things faster; the moisturiser did better on redness control and hydration. But it was not licochalcone A alone, there was no vehicle-only arm, and after two weeks everyone moved onto the test moisturiser.

Early researchAcid

Mandelic acid

Mandelic Acid

A 50-person randomised trial compared a 45% mandelic acid peel against a 30% salicylic acid peel over 12 weeks. Overall acne score improvement did not differ, but salicylic acid did better on non-inflammatory lesions and mandelic acid on inflammatory ones. And adverse effects were fewer with mandelic acid. But nothing was left untreated.

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.

Moderate evidenceAcid

Salicylic acid

Salicylic Acid

Most acne trials used 30% peels performed in a clinic. What Korea allows as an acne functional claim is 0.5%, and only in rinse-off cleansers. There is a sixtyfold gap between those two numbers.

Moderate evidenceAntioxidant

Vitamin C (ascorbic acid)

Ascorbic Acid

In pig skin, L-ascorbic acid entered only when formulated below pH 3.5, and 20% was the concentration for optimal absorption. Pure ascorbic acid is not among Korea's listed whitening actives; four of its derivatives are.

Moderate evidenceHumectant

Hyaluronic acid

Hyaluronic Acid

Holding many times its weight in water is a beaker result. The human trial we found compared it with a ceramide cream in 20 people with atopic dermatitis, and the two products did not differ.

Not establishedRetinoid⚠ In pregnancy Do not use

Hydroxypinacolone retinoate

Hydroxypinacolone Retinoate

The human material we found is one 8-week study of a serum containing retinol, HPR, peptides and silybin. And that abstract states neither the number of participants nor a control group. All the authors work at one cosmetics company's research centre. There is no trial of HPR alone on this page.

Not establishedBarrier lipid

Ceramides

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

In 39 children with atopic dermatitis randomised three ways, a ceramide barrier cream, another prescription cream and an over-the-counter petrolatum ointment did not differ, and the petrolatum was at least 47 times more cost-effective. Applying emollients to newborns to prevent eczema also failed in a Cochrane review.

Moderate evidenceAntioxidant

Bakuchiol

In a 12-week double-blind trial of 44 people, bakuchiol 0.5% and retinol 0.5% reduced wrinkle area and hyperpigmentation to a similar degree, with more irritation on the retinol side. With no vehicle arm, the trial cannot say what the improvement on either side was due to.