Percentages became a marketing device in skincare at the point where shoppers started reading ingredient lists. They look like data. They are printed in a typeface that suggests precision. And in a great many cases they are the least informative number on the pack, because nothing on the pack tells you what the percentage is a percentage of.
What actually decides a percentage
Inside a laboratory, the level of an ingredient is settled by several forces pulling at once, and evidence is only one of them.
- Published evidence. For a small number of well studied materials there is peer reviewed work indicating ranges at which an effect has been observed. This is the strongest input and it exists for fewer ingredients than marketing implies.
- Regulatory limits. Some substances have maximum permitted concentrations set out in the annexes to the cosmetics regulation, sometimes varying by product type or by whether the product is rinsed off.
- Tolerability. A level that works in a trial on a controlled population can be too irritating for general sale, which is a commercial as much as an ethical constraint.
- Stability. Many actives destabilise the emulsion, discolour, or degrade above a certain level, and the maximum stable level may be lower than the maximum useful level.
- Cost. Some actives are expensive enough that a percentage point is a material part of the cost of goods.
- The competitive set. If everyone in a category prints a number, the brand that prints a lower one has to explain itself, and explanation does not fit on a front label.
That last force is more powerful than the industry likes to admit. Once a category has a numbers race, formulators are asked to justify a number rather than to find one.
The central problem: a percentage of what
This is the single thing that turns most front of pack percentages into noise. Many cosmetic actives are not bought by formulators as pure powders. They arrive as trade materials: a solution, a dispersion, a blend with a carrier, or an extract in a solvent. The percentage a brand prints may refer to the amount of that trade material added to the batch, not the amount of the substance you care about.
| What the pack says | What it might describe | What that leaves unresolved |
|---|---|---|
| A percentage of an active | The pure substance as a proportion of the finished product | Nothing, if the pack says so explicitly. This is the useful case. |
| A percentage of a supplier blend | A trade material that may be largely water, glycol or oil | The actual level of the substance, which may be a small fraction of the printed figure |
| A percentage of a botanical extract | Plant material extracted into a solvent at an unstated ratio | The strength of the extract, which is not standardised across suppliers |
None of these three is dishonourable in itself. A blend is often the only practical way to get a difficult material into a formula. The problem is that all three are printed in the same way, in the same size, and a shopper has no means of telling them apart.
20% vitamin C complex
That the finished product contains twenty per cent of something the brand has chosen to call a vitamin C complex. Complex is not a defined term. It may describe a single derivative, a derivative plus supporting ingredients, or a supplier blend sold under a trade name.
The figure itself is not regulated as a claim about efficacy, though the surrounding advertising is.
It does not mean twenty per cent ascorbic acid. It does not mean the product delivers the effect that twenty per cent of any particular substance has been shown to produce. It does not allow any comparison with a competitor printing a different number for a different material.
The pack would have to name the exact substance and state the percentage of that substance in the finished product, in the form used in whatever evidence is being relied on. For example, a named derivative at a stated concentration at a stated pH. Where a brand does this, the number becomes checkable against the published literature.
Why more is frequently not better
For several of the most discussed categories in skincare, the dose response curve is not a straight line. Effect can plateau, and irritation can keep rising after effect has stopped. A formulator choosing a level is often deliberately staying below the maximum, because a product that works and is tolerated for months will outperform a stronger product that is abandoned in a fortnight.
There is a second reason, less often said aloud. Compliance is the largest single variable in whether a skincare routine does anything. A product that stings is used less. A percentage chosen for the shelf rather than for the skin can therefore reduce the real world result while improving the sales figure.
The numbers race in a mature category
Once one brand in a category prints a percentage, the number becomes the axis on which shoppers compare products, because it is the only quantitative thing on the pack. Every competitor then has to print one. Marketing departments ask formulators to reach a number rather than to justify a level, and the level chosen drifts upward across the whole category.
Nobody involved has to act in bad faith for this to happen. It is a structural effect of making one variable visible and all the others invisible.
- The brand that moves first. Owns the comparison and forces rivals to respond on its chosen ground
- The raw material supplier. Sells more material per unit as levels drift upward across a category
- Retail buyers. Get a simple number to put on a shelf edge and in a range review document
- Nobody in particular. Bears the cost, which is a category that is more irritating on average than it needs to be
Described as a market mechanism. No claim is made here about any specific brand or category.
What a formulator checks that a shopper cannot
The level of an active is only one of several things that decide whether it does anything in the pack. The others are almost never disclosed, and they are where the real formulation skill sits.
- pH. Several well known actives only work, or only remain stable, within a narrow pH range. A correct percentage at the wrong pH can be inert.
- Solubility and phase. Whether the active is genuinely dissolved and evenly distributed, or is sitting in a phase where it cannot reach the skin.
- Oxidation and light. Some actives degrade on exposure to air or light, which is why pack choice is a formulation decision and not just an aesthetic one.
- Interaction. Other ingredients can inactivate an active, chelate it, or shift the pH away from its working range over time.
This is why a percentage on its own tells you so little. The number describes what was added. It says nothing about what survived the manufacture, the pack, the warehouse and the first eight weeks on your shelf. What happens over that period is the subject of stability testing.
When a percentage is worth reading
It is worth reading when the pack names the exact substance rather than a category, states what the percentage refers to, and the substance is one for which published evidence exists at a comparable concentration. Under those three conditions you can go to the literature yourself, through PubMed or the Cochrane Library, and see what has been observed.
Outside those conditions, treat the number as branding. That is not cynicism. A percentage printed without a referent is a design element that happens to be made of digits, and reading it as data is the mistake the design is inviting you to make.