Tuesday, January 18, 2011
Adjusting the pH of our products
For the most part, the ingredients we use are pH balanced, so we don't need to mess around much when making lotions, unless we're adding ingredients like AHAs, but when we're working with surfactants, pH is really important.
As you can see from this recipe in which I'm using new surfactants, the first result brings me to 8.6, which is far too high for a body wash. We want something around 6.0 to 6.5, so I adjusted the pH by adding 0.2% citric acid at a time. It took 0.4% citric acid to bring the pH level down from 8.6 to 6.51, which is a good level for our skin.
As a note, I found that 0.15 cc citric acid equals 0.2 grams, so if you don't have a tiny scale, there's a quick and easy way to include it in our products.
In my facial cleanser recipe from the Iron Chemist challenge with LSB, I found the original pH of the mixture was 5.16, which is considered acceptable for our skin's pH range. But I thought it would be fun to try to increase it slightly with the failed batch. I could have used sodium hydroxide (lye) at 10% dissolved in 90% water and add it bit by bit, but I figured this could use more surfactants, so I chose the high pH surfactant decyl glucoside to the mix. 10% decyl glucoside brought the pH to 5.6, so you can see there's quite a change when you use an alkaline ingredient.
If you want to increase the acidity of your product (reduce the pH), I recommend using citric acid at 0.2% a little at a time to decrease it by about 0.9 or so. (It isn't a hard and fast rule that it will reduce it by 0.9 at a time; this was just my experience. It will depend upon the pH of your product, what kind of product it is, what ingredients you've used, and so on.)
If you want to increase the alkalinity of your product (raise the pH), you can use a 10% lye to 90% water solution and add it at 0.1%, test, then another 0.1% if needed, and so on. You can also use triethanolamine (TEA) (pH of 10 to 11) at 0.1% at a time to increase the alkalinity of our products.
Or you can use our ingredients to change the pH level. Adding something like an AHA will decrease your pH, while using a higher pH surfactant - like decyl glucoside or disodium cocoamphidiacetate - will increase the pH.
As a note, if you've made gels with carbomer, you're familiar with the idea of increasing the alkalinity of the product - add some TEA or 18% lye solution to your carbomer and you've got a gel!
Can you tell I'm having fun with my pH meter yet?
As a final point of interest, did you know the term "pH balanced" in commercial products doesn't have a legal definition, so it can mean just about anything. It can mean "pH 5.5, which is around our skin's pH balance" to "blah blah blah". It's on par with saying your skin "appears cleaner", which doesn't actually mean your skin will be cleaner. There's a dental ad on TV right now that claims your teeth will "appear cleaner" but there's no reference point - for instance, appears cleaner than not using a toothpaste at all or another brand of toothpaste? So it really means nothing! And don't get me started on the conditioner ads that have the little asterisk at the bottom of the screen to indicate that they're comparing the state of your hair without using a conditioner (Pantene does this all the time). We all know that using a conditioner will make our hair softer and in better condition! Oh, I didn't realize I was off on a rant again...I better stop.