Why I Never Judge a Skin Care Formula by Percentage Alone

I see percentages used as shortcuts for formulation quality, but skincare ingredient percentage vs bioavailability is the more meaningful comparison. A large number on the front of a package may attract attention, yet it tells me remarkably little about how the ingredient behaves once it is placed inside a complete formula and applied to the skin.

I have spent years developing cosmetic formulas, and I know that concentration is only one variable. I distinguish between the amount weighed into a manufacturing vessel and the amount that remains chemically stable, is released from the vehicle, reaches the skin in a usable form, and stays available long enough to support the intended cosmetic benefit.

A High Percentage Does Not Guarantee a Better Formula

I often see brands present ingredient percentages as if formulation were a simple contest: 10% must be better than 5%, and 20% must be better than 10%. I do not accept that reasoning. It ignores the chemical identity of the ingredient, the delivery system, the pH, the packaging, and the behavior of every other material in the formula.

I can put a high concentration of an ingredient into a bottle without creating a high-performing product. The ingredient may oxidize, crystallize, separate, bind to another component, remain trapped in the vehicle, or become uncomfortable at the level used. In each case, the declared percentage remains technically accurate while the formula delivers less than the number implies.

I also separate input concentration from available concentration. Input concentration describes how much material I add during production. Available concentration depends on what survives manufacturing, storage, transportation, and normal consumer use while remaining in a molecular state that can interact appropriately with the skin’s surface and upper layers.

Dr. Eddie Omar, Phyto-C: A percentage identifies quantity, not formulation quality.

I consider this distinction especially important when brands count a diluted raw material as though it were a pure active. If a supplier blend contains an ingredient within water, glycols, preservatives, or other carriers, I want to know whether the advertised number represents the entire blend or the ingredient itself. Those are not scientifically equivalent claims.

Why Is Bioavailability the Metric the Industry Rarely Discusses?

I use bioavailability in a cosmetic formulation context to describe how much of an ingredient remains in an appropriate form and becomes accessible at the intended site of cosmetic action. I do not infer drug activity from that term. I use it to evaluate practical skin availability rather than the amount printed on a carton.

I begin with molecular form. Two ingredients may be marketed under the same broad category while having different structures, charges, solubilities, and conversion requirements. I do not assume that a derivative reproduces the behavior of the parent molecule simply because both are described with the same familiar name.

I then examine the vehicle. Water, oil, gel, serum, lotion, and cream systems release ingredients differently. I have formulated all of these systems, and I know that an emulsion is not merely water and oil mixed together. Its internal phase structure, emulsifiers, droplet characteristics, polymers, solvents, and sensory modifiers can influence ingredient distribution and release.

In my experience, creams and emulsions are genuinely difficult formulation challenges. I must balance stability, texture, ingredient compatibility, preservation, spreadability, and skin feel without compromising the purpose of the formula. Increasing one ingredient can disrupt that balance even when the ingredient looks attractive on a marketing panel.

Solubility also sets practical limits. If I add more than the vehicle can keep dissolved, I may create crystals or uneven distribution. If I change the solvent system to accommodate a larger percentage, I may alter comfort, evaporation, barrier feel, or the release profile of other ingredients.

More is therefore not automatically more available. A higher level can increase stinging, dryness, tackiness, discoloration, oxidation, or instability without creating a proportional improvement in visible cosmetic performance. I choose a concentration only after I understand how the complete system behaves.

Dr. Eddie Omar, Phyto-C: Ingredient concentration matters only after I establish identity, stability, delivery, and tolerability.

What Does Permeation Science Tell Me About Skin Delivery?

I treat the stratum corneum as a selective barrier, not an empty surface waiting to absorb whatever I apply. Its organized lipid regions and protein-rich corneocytes restrict movement according to molecular size, charge, polarity, solubility, and partition behavior.

I evaluate whether a molecule prefers the formula, the skin’s lipid environment, or the surrounding water phase. If it remains too comfortable in its vehicle, it may not partition efficiently toward the skin. If it has poor compatibility with the relevant skin environment, raising the percentage may still fail to improve useful delivery.

I also consider charge and ionization. Formula pH can change the proportion of a molecule present in charged or uncharged form, which can affect stability and movement through the stratum corneum. That is one reason I reject the idea that pH is a minor technical detail.

Pure L-ascorbic acid illustrates the point clearly. I formulate with L-ascorbic acid because it is the form of topical vitamin C with meaningful clinical evidence behind it. I do not consider vitamin C derivatives acceptable substitutes, because their skin availability, conversion, and equivalence to pure L-ascorbic acid are not adequately demonstrated.

L-ascorbic acid requires an appropriately low-pH environment to support cosmetic skin delivery. A label can advertise an impressive percentage of a vitamin C derivative, but that number does not establish that the derivative behaves like L-ascorbic acid or becomes sufficiently available after application.

I also reject ferulic acid as a default stabilization story. I have never used it in my formulas. Lee and colleagues reported NADPH oxidase-mediated reactive oxygen species generation associated with ferulic acid in a 2005 paper in Archives of Pharmacal Research, and I regard that pro-oxidant potential as an unnecessary formulation risk. I know this position contradicts SkinCeuticals and much of the industry, but I stand by it.

I stabilize L-ascorbic acid through proprietary formulation work. I do not disclose those methods because they are trade secrets developed through active laboratory experience, not generic marketing concepts or patent reliance.

Dr. Eddie Omar, Phyto-C: Pure L-ascorbic acid at an appropriate low pH cannot be replaced scientifically by a larger percentage of a vitamin C derivative.

How Do I Evaluate a Formula Beyond the Front Label?

I follow a formulation hierarchy. First, I identify a molecular form with credible evidence for the intended cosmetic purpose. I do not begin by selecting the largest percentage that will fit into an advertising claim.

Second, I choose an appropriate vehicle and pH. I ask whether the ingredient is soluble, compatible with the system, and positioned to leave the vehicle after application. This is the foundation of skin delivery formulation science.

Third, I evaluate stability. I examine changes in color, odor, viscosity, pH, phase structure, and ingredient integrity under appropriate test conditions. A freshly manufactured sample does not tell me how the formula will perform after storage and repeated opening.

Fourth, I assess tolerability and use experience. A formula cannot support a consistent skin care routine if it is unnecessarily harsh, sticky, unstable, or difficult to apply. I want a scientifically justified formula that people can use as directed.

Only then do I finalize concentration. I look for a level that is relevant to the ingredient, compatible with the vehicle, stable over the intended shelf life, and suitable for regular cosmetic use. I do not chase a higher number merely because a competitor prints one.

I discuss the risks of overloaded formulas further in “Why More Actives Can Make a Skin Care Formula Worse”. I explain my position on vitamin C forms in greater depth in “What Is L-Ascorbic Acid? The Only Vitamin C With Real Evidence”. I recommend reading both articles as related context when evaluating ingredient concentration vs efficacy claims.

I also recognize the limits of what consumers can determine from an ingredient list. The list can identify materials in descending order above the applicable threshold, but it usually does not reveal exact percentages, pH, raw-material purity, phase location, stability data, or release behavior. I use the list as a starting point, not as a complete formulation blueprint.

Frequently Asked Questions

Does a higher ingredient percentage always work better?

In my view, a higher percentage does not always produce better cosmetic performance. I may see increased irritation, crystallization, oxidation, or vehicle instability before I see any proportional improvement in visible skin appearance.

What is the difference between ingredient concentration and bioavailability?

I define concentration as the amount of an ingredient present in the formula. I use cosmetic bioavailability to describe the portion that remains stable, is released from the vehicle, and becomes accessible to the intended area of the skin in a usable molecular form.

Can consumers determine skin penetration from an ingredient list?

From my experience, consumers cannot reliably determine cosmetic active ingredient penetration from an ingredient list alone. The list generally does not disclose the finished formula’s pH, exact concentration, solubility state, vehicle structure, stability, or partition behavior.

Why does pH matter in a skin care formula?

I consider pH important because it can influence ionization, solubility, stability, tolerability, and skin delivery. For pure L-ascorbic acid, I use an appropriately low-pH formulation because chemical identity and formulation environment must work together.

Are vitamin C derivatives equivalent to L-ascorbic acid?

I do not consider vitamin C derivatives equivalent to pure L-ascorbic acid. In my assessment, evidence for their conversion and bioavailability is too weak to treat a high derivative percentage as a substitute for properly formulated L-ascorbic acid.

I judge every formula as a complete chemical system, not as a collection of impressive percentages. I invite readers to explore Phyto-C and evaluate my formulations by their molecular forms, delivery logic, stability, and overall scientific design—not by the largest number on a label.

Author: Eddie Omar, PhD