Why concentration — not the ingredient list — decides what your skincare actually does
Turn over our Prep Pad and read the label, and you'll find three ingredients that look like they belong in an exfoliating acid toner: apple extract, lactic acid, and citric acid. A reasonable person would conclude that the Prep Pad is a chemical exfoliant. Actually, not one of those three ingredients is exfoliating your skin in this formula. One is pulling water into your skin. One is reinforcing your skin's own moisture chemistry. One is engineering the formula itself. Even though these are technically the same molecules you'd find in a peel, on this formula they are doing a different job. Our ingredient obsession at L16 might be your ingredient obsession as well, once you understand exactly what each ingredient is doing and why.
An ingredient name tells you what a molecule is, not what it's doing. What it's doing is determined by dose and context. How much of it is in the formula, what the formula's pH is, and what else is in the bottle. Chemistry works. The FDA's own guidance on alpha hydroxy acids notes that the extent of exfoliation "depends on the type and concentration of the AHA, its pH, and other ingredients in the product." Cosmetic chemists formulate around this constantly: AHAs need a formulation pH of roughly 3.5–4.5 for meaningful exfoliant activity, because pH determines how much of the acid exists in its active "free acid" form. Shift the concentration or the pH, and the very same molecule stops resurfacing skin and starts doing something else. A molecule at 10% in a pH 3.5 formula and the same molecule at 1% in a pH 5 formula are, functionally speaking, two different ingredients.
With that principle in hand, let's walk through the three "acids" in the Prep Pad — and why none of them is doing what you might think.
Apple extract, the humectant in exfoliant's clothing
Apple extract carries AHA associations because apples contain malic acid, a genuine alpha hydroxy acid. So when consumers see it, many assume fruit-acid exfoliation.But look at what apple extract actually is, compositionally: mostly natural sugars — fructose, glucose, sucrose — plus polyphenols and pectin. Those sugars are the operative part. They are humectants: hygroscopic molecules that attract water and bind it in the upper layers of the skin, which is why ingredient references classify apple fruit extract's primary function as humectant. The clinical data points the same direction. A 28-day human study published in the Journal of Cosmetic Dermatology found that creams containing standardized apple fruit extract significantly increased skin hydration, with hydration rising as extract concentration rose, while transepidermal water loss and skin pH stayed essentially unchanged. That signature (more water in the skin, barrier undisturbed) is the fingerprint of a humectant, not an exfoliant.
In the Prep Pad, that's precisely the job apple extract was hired for: boosting hydration. The trace fruit acids that ride along in an extract are nowhere near exfoliating territory. Which brings us to the ingredient people ask about most.
Lactic acid — the same molecule, two careers
Lactic acid has a genuinely split professional life, and dermatology is clear about where the split falls. At meaningful concentrations in a low-pH formula, lactic acid is a real exfoliant. A controlled study comparing lactic acid at 5%, 10%, and 15% — and separately at pH 2, 3, and 4 — found that both concentration and pH shape its effect on desquamation and epidermal turnover. That's a range where exfoliating activity has been studied, not a single switch that flips on at one fixed percentage. Exfoliation emerges gradually as concentration and acidity increase together.
Somewhere below the concentrations studied for exfoliation, lactic acid doesn't go idle — it changes jobs. At higher concentrations, lactic acid works well as an exfoliating ingredient to break up connections between skin cells, while at lower concentrations, it works as a humectant, which means it has the ability to pull water into the outer layer of the skin. There's an elegant biological reason this works. Lactate is a native component of your skin's natural moisturizing factor, the cocktail of amino acids, PCA, urea, and lactate that binds water and keeps skin hydrated even in dry air. Low-dose lactic acid isn't a watered-down peel. It's a top-up of something your skin already manufactures to hydrate itself.
That is exactly its role in the Prep Pad: the lactic acid in our blend sits at a low concentration, well under the ranges studied for exfoliating activity above. It is there as a humectant, working alongside the apple extract, not performing a gentler version of a peel. If a formula's lactic acid content won't exfoliate, we think you deserve to know that before you buy it expecting resurfacing.
Citric acid, the ingredient that isn't really for your skin at all
Citric acid may be the most misread ingredient in all of skincare. Yes, it's technically an AHA. But in the overwhelming majority of products, ours included, it isn't there to treat your skin. It's there to tune the formula. Citric acid's functions in cosmetics as a pH adjuster, chelating agent, or fragrance ingredient, exfoliation doesn't even make the list of standard uses. At the fractions of a percent used for pH adjustment, formulators add citric acid to pull a product's pH down into the mildly acidic range that skin prefers. That's a meaningful job: healthy skin surface is naturally acidic. A well-adjusted pH keeps a formula compatible with your acid mantle and keeps the other ingredients stable and working.
In the Prep Pad, citric acid appears at very low levels, doing exactly one thing: nudging the formula's pH closer to skin-neutral.
The beauty industry has a name for exploiting the gap between what's in a formula and what's functional in it: “angel dusting”, which is adding a trace of a trendy active so it can legally appear on the label and in the marketing, at levels far too low to do anything. The labeling rules make this easy to hide. U.S. regulation requires ingredients to be listed in descending order of predominance — but everything at 1% or less can be listed on a label. Concentrations are never disclosed. So a label tells you what's present, roughly ranked, and nothing about whether any of it is present at a level that matters.
How to read a label like a formulator
You can't measure concentrations from your bathroom shelf, but you can get surprisingly far with four habits:
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Ask what job each ingredient is plausibly doing, not just whether it's present. An acid near the end of a list is far more likely to be adjusting pH or hydrating than exfoliating.
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Use the 1% marker trick — but don't over-trust it. Preservatives like phenoxyethanol or sodium benzoate are almost always used at about 1% or less. Any "hero" ingredient listed after them is likely at a fraction of a percent. This narrows the range; it doesn't reveal an exact number.
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For actives with studied concentration ranges, ask for numbers. Lactic acid's exfoliating activity has been evaluated across roughly 5–15% in the published research. If a product sells itself on an active and won't say anything about its concentration, treat the claim as decoration.
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Ask the brand what each ingredient is for. A brand that knows its formula can answer for every ingredient.
The Lenox and Sixteenth position
We built Lenox and Sixteenth on a simple bet: that smart customers, given real information, buy better. That’s why we'll tell you when an acid in our formula isn't exfoliating, and what it's actually doing instead. The Prep Pad's apple extract hydrates. Its low-dose lactic acid hydrates the way your skin's own chemistry does. Its citric acid tunes pH. No hidden functions, no borrowed reputations, no letting a label imply what the chemistry can't deliver. If that's how you'd rather shop for your products — you know where to find us.