Dear Holly,
I have a skin question. I read recently that alpha hydroxy acids will not work if they are in a "pH balanced" formulation. Is this true? If so, how can I tell if I am spending a lot of money for a product that won't work? Can I change their pH and make them effective?
PG.
Dear PG,
What you read is true. Alpha hydroxy acids will not be in an active (acidic) form if they are "pH balanced", or in other words, neutral, at pH 7. Some of these products are quite expensive, and I was surprised to learn that a portion of even the expensive products do have a pH which renders their effectiveness questionable.
The reason I took a while to answer your question is because I wanted to buy a number of products and test them. At work I can use a pH meter, but in my kitchen I use simple litmus paper which is readily available off the Internet to buy, and it ought to be dirt cheap. I buy mine from a local beer making supply store, and normally use it in testing wine that I make. You can get your own litmus paper and test your sample, so you can do the same. I'd get a couple of types for ranges of values below 7 if you are testing your products.
If the opacity of the formulation is a problem, try diluting the material 1:10 in water, preferably freshly opened distilled water. (Carbon dioxide from the atmosphere dissolves into standing water and normally makes water a wee bit acidic.) The alpha hydroxy acids are water soluble and will leach out into the water. Then, the pH that you measure will be higher (more basic) than the true value by one unit, (since pH is a log scale and you diluted by ten.) So if you do dilute the material tenfold, subtract 1 from the pH that you measure. This should get you a crude estimation of the pH.
But what pH do you want?
In order for half of the alpha hydroxy acid present to be in the active, acidic form, the pH of the solution must be equal to something called the pKa of the acid. Acids have different pKa values, it is a measure of how strong they are (the lower the number the stronger they are.) If any of my three readers out there (excluding my mom) are dying to know more about pKa values you can read my review of acid base chemistry. Here are some common alpha hydroxy acids and their pka values. You can see most are around 3.
glycolic acid 3.74
lactic acid 3.08
malic acid 3.40
tartaric acid (meso form) 3.22
alpha-tartaric acid 2.98
citric acid (has three acidic regions on it, and all three have different pka values: 5.19, 4.77, and 3.15.
You could always lower the pH of your formulation and make it more acidic. Acidic solutions, by definition, contain an excess of hydrogen (H+) ions. So why not buy a bottle of hydrogen ions and add them? Well, you can't! That is because a bottle of hydrogen ions doesn't exist. Ions of like charge repel each other. The next best thing to do is add something that is not charged, which can release hydrogen ions.
An acid is something that can release hydrogen ions (or split water in two and hold onto one half of water and release the rest as a hydrogen ion.) You can always make your formulation more acidic by adding some mild acid, like a few drops of vinegar, lemon juice, citric acid, or ascorbic acid (but not ascorbate, that is a base.) This would certainly make it more powerful. But I must really caution you about that!
Maybe there is a good reason why the company wanted only a minuscule amount of the alpha hydroxy acid to be in the active form. The acids work, scientists believe in part, by breaking down junctions (desmosomes) between dead skin cells. This allows dead cells in outer skin layers to be removed, and it does seem to stimulate growth of cells below, and their manufacture of water-attracting molecules like hyaluronic acid and reinforcing ones like collagen. But the process can be irritating, and you can end up looking worse than before, with reddened, irritated skin.
You are supposed to apply sunscreen religiously if you use such products, (actually it is a good idea to do so daily, anyway.) The more powerful preparations are applied by a dermatologist, not at home. So although it is theoretically possible to make your preparations more active, I don't advocate placing a lot of active acid on your face without a dermatologist administering them.
Finally, if anyone is wondering why the pH can render an acid effective or ineffective, here are some chemical details:
Alpha hydroxy acids are quite popular in skin formulations these days. They are just organic acids, with a particular structural modification. Let me first show you what any organic acid looks like:
The "alpha hydroxy" designation just means that there is something called a hydroxyl group (O bonded to H) connected to the "alpha" carbon. The alpha carbon of an acid is the carbon that is immediately bonded to the carbon in the square, above. (Sometimes skin products have beta-hydroxy acids, which means that the hydroxyl is bonded to a carbon that is attached to the alpha carbon, the next carbon over.) Chemists use this alpha-beta whatsis language to tell each other how the molecule is constructed and what is bonded to what.
But what makes any organic behave like an acid is the H in the square in the picture. An acidic solution is full of H+ ions, and acids are capable of releasing H+ ions--if they are in the right environment.
But if you place an acid in a more H+ deficient environment, like a neutral or basic one, its H+ is likely to leave, and what is left behind is not an acid anymore, and will not work as an acid.
