click here for more information on my lovely pH meter) and I've written a bit about how to adjust pH in surfactant based products in the past, but I thought I'd address the issues of pH and lotions.
For the most part, we don't need to adjust the pH of our lotions as most of our ingredients have a neutral or slightly acidic pH, like our water, hydrosols, oils, and butters. If you want to make a lovely body butter or foot cream, don't worry about the pH as it's likely to be around 6, which is a good level for our skin. Just make the lotion and enjoy the moisturizing goodness.
But if you're using cosmeceuticals, you will need to adjust the pH for some of the ingredients to work properly. We can do this by adding 0.2% citric acid during the cool down phase and testing the pH. If you need to lower it further, add another 0.2% citric acid until you reach the optimal amount.
As well, some of our cosmeceuticals have acidic pH levels and you'll have to increase the pH level to get it to a good level. You can do this by adding sodium hydroxide (also known as lye), which is very alkaline. Dissolve 10% sodium hydroxide in 90% water and add this at 0.1% at a time in the cool down phase, testing after every addition.
You can use apple cider or other vinegars to reduce the pH, but the smell is a bit much for some people (like me!). I can't offer any suggestions about how much vinegar to use as I only tried it the once and I didn't have a pH meter then. As with most things in lotion making, it'll be trial and error to figure out how much you need in your product.
It's hard to predict how much of an ingredient will affect the pH of your lotion (you could work on a formula for it, but it's easier just to test the pH as we add various ingredients). Will adding 1% AHA or 5% Multifruit BSC reduce the pH of your moisturizer to 3.5? Probably not, but it's hard to tell as most of our ingredients aren't as standardized as we think. The only real way to tell what an ingredient will do to the pH of a product is to include said ingredient, then test! And the only way to know how much citric acid or lye to add to the product is to test the pH, decide whether the pH must go higher or lower, then add the acid or alkaline at 0.2% in the cool down phase and test again.
Join me tomorrow as I catch up from my week of exciting illness with more on cosmeceutical ingredients! (I have a good list going, but if you have other ideas, please comment below!)