A product description that leads with "hyaluronic acid", "niacinamide" or "peptides" is asking you to transfer what you know about an ingredient to a particular jar. Sometimes that transfer is reasonable. Often it is not, and telling the difference is a useful skill for anyone buying, developing or selling skincare.
This article is written for business readers assessing products and supplier claims. It is not advice on treating any skin condition. If you have a specific concern about your skin, speak to a qualified professional.
Start with the ingredient list
In Great Britain, cosmetic ingredients must be listed in descending order of weight, determined when they are added to the product. Ingredients below 1% may be listed in any order after those above 1% (OPSS guidance). Labels use standardised ingredient names, so "niacinamide" or "sodium hyaluronate" should appear as such.
The order gives useful clues, but no exact figures. An ingredient near the top is likely to be present in a meaningful amount. One near the end may be present at a very low level, but you cannot tell where the 1% threshold falls from the label alone. Note also that an ingredient can appear on the list without being the source of the effect claimed on the front of the pack.
What a percentage does and does not tell you
Some brands disclose a percentage, such as "5% niacinamide". That is more informative than a name alone, but ask two questions.
- Percentage of what? Some ingredients are supplied to manufacturers as solutions or blends. A stated percentage may refer to the pure substance or to the supplier's blend. Ask which.
- Is that the concentration that was studied? Research on an ingredient is tied to the concentrations and formulations tested. A product with a different amount, in a different base, is not covered automatically.
More is not necessarily better. Tolerability, stability and the rest of the formula all matter, and a higher figure can be a marketing choice as much as a technical one.
Formulation context
Three aspects of the formula often decide whether an ingredient can do what is claimed.
Can it reach where it needs to act?
The skin is designed to keep things out. In an influential 2000 paper, Bos and Meinardi argued that a compound's molecular weight generally needs to be under 500 daltons for it to be absorbed through skin. They based this on the observation that common contact allergens and topical drugs fall below that size (Bos and Meinardi). It is a rule of thumb, not a law, and formulation can influence penetration. Even so, it is a useful prompt when a claim implies that a large molecule works deep in the skin.
Is it stable in this product?
An ingredient that degrades before use cannot deliver much. A 2021 study tested retinoids in 12 commercial cosmetic products over six months. It reported declines of 0% to 80% at 25°C and 40% to 100% at 40°C, found that light degraded them more than temperature, and found that some products contained less than declared (Temova Rakuša et al.). The study concerned retinoids, but the lesson is general: stability depends on the formulation and its packaging, not just the ingredient.
Is the rest of the formula doing the work?
Moisturising bases, occlusive ingredients and humectants can all improve how skin looks and feels. If a product "with peptides" shows improved hydration, the base may deserve much of the credit.
Ingredient evidence versus product evidence
This is the most important distinction in the article. A study showing that an ingredient did something, in a particular formula, at a particular concentration, in particular people, is evidence about that test. It is not automatically evidence that another product containing the ingredient will do the same.
UK advertising rules reflect this. The Committee of Advertising Practice advises that efficacy claims for beauty products need to be supported by tests on people, and notes that laboratory (in vitro) studies have frequently been dismissed as inadequate (ASA and CAP). Its guidance adds that consumer perception tests suit claims such as "skin feels smoother", but cannot support objective claims such as a measured reduction in wrinkles.
Cosmetics law points the same way. In Great Britain, cosmetic claims must meet common criteria that include legal compliance, truthfulness, evidential support, honesty, fairness and informed decision-making. The Product Information File must include proof of the effect claimed where the nature or effect of the product justifies it (OPSS guidance).
Three ingredients, three kinds of evidence
The following summaries are drawn from the study abstracts. They illustrate how to read evidence, not what any particular product will achieve.
Niacinamide
In a 12-week, double-blind study, 50 women with signs of photoageing applied a 5% niacinamide product to one side of the face and a vehicle control to the other, twice a day. The authors reported reductions in fine lines and wrinkles, hyperpigmented spots, red blotchiness and sallowness, and improved elasticity (Bissett et al., 2005).
The design has real strengths: each participant served as her own control, and the study was randomised and double-blind. The limits are equally clear. The sample was small, the test used one concentration in one formula, and the participants are described as white women, so the results may not generalise to everyone. A 2% serum, or a 10% one, is a different product.
Hyaluronic acid
A 2011 study gave 76 women aged 30 to 60 a cream containing 0.1% hyaluronic acid of one of five molecular weights, from 50 to 2,000 kilodaltons. They applied it around one eye twice a day for 60 days, with a vehicle cream around the other eye. All the hyaluronic acid creams improved skin hydration and elasticity compared with the vehicle. Wrinkle depth improved significantly only in the 50 and 130 kilodalton groups, which the authors suggested might reflect better penetration of the smaller molecules (Pavicic et al., 2011).
Two practical points follow. "Hyaluronic acid" is not one thing: molecular weight changed the result, so ask which grade a product uses. And even 50 kilodaltons is far above the 500-dalton guide discussed earlier. The authors' explanation for the wrinkle result is a hypothesis, not settled fact.
Peptides
"Peptides" is a family, not an ingredient. A 2009 review grouped topical peptides used against skin ageing into four categories: signal peptides, enzyme-inhibitor peptides, neurotransmitter-inhibitor peptides and carrier peptides. It then reviewed controlled studies for each (Gorouhi and Maibach, 2009). A claim that simply says "with peptides" tells you little. Ask which peptide, under its ingredient name, which study supports it and at what concentration.
Reading a study quickly
You do not need to be a scientist to ask good questions of a study. We suggest checking:
| Question | Why it matters |
|---|---|
| Was the finished product tested, or an ingredient? | Ingredient data does not automatically transfer to another formula. |
| Was there a control or placebo? | Without one, improvement may come from the base, the season or simple expectation. |
| How many people, for how long? | Small, short studies are more easily swayed by chance. |
| What was measured, and how? | Instrument measurements and self-assessment answer different questions. |
| Who carried it out and funded it? | Industry studies are common and can be sound, but declared interests are part of the context. |
| Is it published and traceable? | A citable paper can be checked. "Clinically proven" on a brochure cannot. |
Questions to ask about a claim
- Which exact claim do you intend to make, and what is the supporting evidence for this finished product?
- If the evidence concerns an ingredient, at what concentration and in what type of formula was it tested?
- Does a stated percentage refer to the pure ingredient or to a supplied blend?
- For hyaluronic acid, which molecular weight or grades are used? For peptides, which peptides?
- Is there stability data showing the ingredient remains at the declared level over the product's shelf life?
- Can the study be shared, and who conducted it?
Good suppliers welcome these questions, because clear answers protect them as well as you. Where evidence is thin, the honest response is to make a more modest claim, one about how the product feels or looks, which consumer testing can properly support.
