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.

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 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.

Ingredient dataOther

Adenosine

At 0.04% a product can be filed as a wrinkle-improvement functional cosmetic without submitting data. But the only human trial we found in the published literature had 22 participants, and its comparator was not vehicle but another adenosine formulation.

Moderate evidenceBarrier lipid

Panthenol

In a three-week study of 23 people on deliberately damaged skin, the reduction in transepidermal water loss was larger than control (−168.36 vs −123.38 g/m²/h, P = .023). What that control was, the abstract does not say.

Moderate evidenceSoothing

Centella asiatica

Centella Asiatica Extract

In a split-face trial of 30 people after laser resurfacing, the side treated with Centella extract gel showed a lower erythema index (coefficient −0.03, P = .046) and better crusting and wound appearance in the first days. Skin biophysics, though, did not differ between the two sides.

Moderate evidenceOther

Tea tree oil

Melaleuca Alternifolia Leaf Oil

In a double-blind trial of 60 people using a 5% gel for 45 days, total lesion count and acne severity improved significantly more than with placebo — 3.55 and 5.75 times more, respectively. It is one trial, and 45 days is short.

Moderate evidenceHumectant

Glycerin

In a double-blind crossover study of 51 people with dry skin, the finished emollient reduced transepidermal water loss more than the vehicle and more than the vehicle plus glycerol. Moisturising is the work of a formula, not of one ingredient.

Early researchOther

Arbutin

The Korean listed amount is 2–5%. In a split-face pilot in 30 people with melasma, alpha-arbutin 5% plus kojic acid 2% did not differ from a prescription triple-combination cream on objective measures, and relapse was worse on the triple-combination side.

Ingredient dataSoothing

Alpha-bisabolol

Bisabolol

The Korean listed amount is 0.5%, the lowest of the nine whitening actives. But we could find no human trial comparing this ingredient on its own against vehicle. What turns up are studies of multi-ingredient formulas.

Not establishedHumectant

Collagen

The rule of thumb in the skin-penetration literature is 500 daltons. Collagen is hundreds of times larger. That applying it increases collagen in the dermis has not been established in people.