How concentration makes AHAs and BHAs more effective in skincare
We know that alpha and beta hydroxy acids are great for our skin. They can help treat acne, reduce sebum production, and even combat signs of aging. The reason they’re so effective is because they’re acidic, just like our skin. Matching acidity means AHAs and BHAs can penetrate through the skin’s acid mantle to work on the deeper cells underneath, where they can be more effective. However it’s important to factor in the pH and concentration of both individual ingredients, and the final formulation, when using acids in skincare. This ensures optimal results, and minimizes unwanted side effects.
How acids and pH work
The pH scale measures if a substance is acidic or alkaline (base). Water is neutral, pH 7. Acids range from pH 6-0, and bases from pH 8-14. Each number on the scale increases or decreases by a factor of 10, so pH 5 is ten times more acidic than pH 6, and so on.
What you might not know is that the pH number assigned to a substance only applies in one particular circumstance — when that substance is dissolved in pure water at 25oC (77oF). This gives us a standard measure, but the actual pH of any substance will change depending on factors like its concentration, temperature, and other ingredients it’s combined with.
For example, alpha and beta hydroxy acids are all around pH 3-4, about the same as soda or vinegar, and slightly more acidic than our skin. However skin peels made with solutions of 30-70% glycolic acid can be as acidic as pH 0.08 – that’s as strong as stomach or battery acid!
How acid concentration affects pH
One reason for this difference is the concentration. In chemistry, concentration refers to how much of a substance is made of one particular ingredient. For example if you buy a serum that’s 8% glycolic acid, that means for every 100 molecules of that serum, 8 of them are glycolic acid. An 8% concentration is twice as strong as a 4% concentration, or half the strength of a 16% concentration, and so on.
We all want products that contain the highest concentration of key ingredients. If you purchased a “cocoa butter body wash” and discovered it was only 0.5% cocoa butter, you’d be annoyed! However there is often a trade-off between including effective ingredients in products and avoiding negative side effects, such as making a formulation too strong to handle.
Most topical skincare products contain concentrations of about 8%. The FDA recommends that AHAs not be more than 10% concentrated, and delivered in formulations of pH 3.5 or higher. If you want to use stronger acids for a more dramatic effect, it’s best to visit a dermatologist who knows how to apply (and remove!) them safely.
AHAs and BHAs can be used in skincare formulations to lower the overall pH of a product. This is important because some products aren’t acidic at all. For example soap is usually around pH 9-11. Because our skin is naturally acidic, adjusting the pH of a formulation to match produces the best results.
How concentration and pH affect free acid values
The concentration and pH of fruit acids in skincare don’t just affect the overall acidity of the product, but also something known as the free acid value. This is calculated using something called the dissociation constant.
PH stands for “potential of hydrogen” (sometimes called “power of hydrogen”). It’s a measure of how many hydrogen ions a substance can emit under specific circumstances. The dissociation constant is a measure of how likely the substance is to give up those ions. It’s written as pKa. Substances with more ions are more likely to give them up, so there’s a link between the number of ions (pH) and the likelihood of giving them up (pKa). These two measurements are very similar, but not exactly the same.
An acid molecule that still has its ions is known as a free acid. An acid molecule that has given up its ions is known as a dissociated or ionized acid. When pH and pKa are equal, the molecules are 50/50 free and ionized. Altering the pH can make the acid more or less likely to become ionized. For example the pH of glycolic acid is 3.83, so when the pKa is also 3.83, the acid is 50/50 free and ionized. However if glycolic acid is delivered in a formula that is 2 pH, 98.5% of the acid is in its free form. If the pH is increased to 6, only 0.67% of the acid is free.
Whether or not an acid molecule is free or ionized is important because free acids work much more effectively on our skin. Ionized molecules don’t absorb through the acid mantle to the lower cells, so they only have limited effects. That means to produce the best results, skincare products need to balance concentration and pH. A 2% concentration of glycolic acid, delivered at 3.5 pH, contains much higher levels of free acid than a 10% concentration in a 6 pH formula.
This can produce misleading results, because most of us assume that more of an ingredient will deliver better results. Given a choice between two glycolic acid products, one with a 2% concentration and one with 8%, you’d probably pick the 8%. But depending on the overall pH of the formulation, the 2% product might actually be stronger and more effective.
How acid concentration affects skincare results
Because the amount of free acid molecules changes based on concentration and pH, the effects produced by AHAs/BHAs can also be adjusted. Different concentrations and pH can tailor results to address specific skin complaints or reduce irritation for sensitive skin. For example glycolic acid can firm skin and tackle sun damage when used in concentrations above 5%. Lactic acid hydrates at 2% concentration, and exfoliates at 5-10%. Malic acid is most effective when used in low concentrations (1-2%) in conjunction with other AHAs. And citric acid needs high concentrations to produce exfoliating effects, but its low pH increases the likelihood of irritation when used extensively.
Each acid must therefore be delivered in the most optimal concentration and pH in order to get the desired effects, and just a small change in pH and/or concentration can make a big difference to the potency of a skincare product. That’s why it isn’t enough to rely on simply choosing a product with the highest concentration of key ingredients in order to get the best results.
At Qyral, every formulation is pH and concentration adjusted for each individual to deliver the best results possible. This also ensures that your skincare products always work in predictable ways to support and nourish your skin.