Our skin has an acid mantle, which is a fine, slightly acidic film with a pH of 4.7 to 5.9, which acts as a barrier to bacteria, viruses, and other icky things that might penetrate our skin. This acid mantle is a result of production of amino acids and lactic acid that settles on our skin. It's a good environment for good bacteria and other tiny creatures, and they can protect us from chemical and natural attack by other tiny creatures or skin unfriendly chemicals. Out of whack pH levels can lead to an increase in scaling, a decrease in hydration, and a possible increase in bacterial and yeast infections.
We don't want to mess with the acid mantle, so we need to formulate our products within the skin's pH range - a pH of 4.5 to 6-ish is good for leave on products. We don't want to use harsh surfactants or very alkaline soaps as they can destroy the acid mantle, which leads to dry skin, reduction in the stratum corneum lipids, and lowered resistance to microbial or chemical assaults.
For facial products, shampoo, and body washes, we want to keep the pH lower than 6, between 4.5 and 5.9 for leave on products.* This means the products we are making will be acidic. Most of the ingredients I have chosen for this first part of the facial products series are acidic. (There are a few exceptions and you'll see them in the next few days...)
As a note, products like facial peels or glycolic acid masks will have a much lower pH, but we aren't formulating those things at home!
Most of our surfactants are in the perfect zone for pH. For example, Stepan's Mild-LSB has a pH of 6.0 (10% in water), while Stepan's Amphosol CG (cocamidopropyl betaine) has a pH of 5 to 7 when it's at 10% in water. (I'll get into more detail with you about this shortly...)
The recipes I share with you on this blog are always pH balanced so you can make them at home without having to use a pH meter. If you alter the recipe and include things that are more acidic - like AHAs - or more alkaline - like liquid soap - you will change the pH. It may or may not make a huge difference. It's hard to tell without a meter.
What about pH strips? They're okay. They offer a general idea of the pH of the product - say 5 to 6 - which can be good enough when we are making most of our products. Where they aren't great is when we get into using cosmeceuticals and extracts with wacky pHs.
Related posts on pH:
pH of our skin (part one)
pH of our skin care products
pH and the skin's acid mantle
Weekend Wonderings: You can't have alkaline skin
Adjusting the pH of our products
Other posts in this series:
Newbie Tuesday: We're making facial products!
Let's start making facial cleansers! - Your skin type
Surfactants - what are they?
Okay, so we're ready to take a look at our surfactants! Join me tomorrow for more fun formulating facial cleansers!