When creating skin care products, we want to formulate most of our products with a pH range of 4.7 to 6. One huge exception to this rule is handmade soap, which, by definition, is alkaline. Soapmakers compensate for the higher pH by superfatting, using more oil than necessary to create a more moisturizing and cleansing product. Another is the use of saponified fatty acids – usually a combination of stearic acid with triethanolamine to create a soap – as an old fashioned emulsifier for cold cream type lotions, which results in a more alkaline lotions. (This saponification can be the cause of the soaping effect or white layer you notice in some lotions.)
 
Hair is also acidic. Virgin hair will have a lower, more acidic pH, while damaged hair will have a higher, but still acidic, pH. Each hair strand is covered in a layer of hydrophobic (water hating) fatty acids that repel water from entering the hair shaft. Alkaline ingredients can damage that layer, allowing water to enter the strand. The cuticle isn't one flat sheet, but little overlapping scales that look a lot like shingles on a roof. When the strand swells, these little shingles lift up, and they can catch on other ones causing tangles. There’s an increase in friction, which can lead to damage like the cuticle tearing away from the hair strand.
 
As the pH of hair increases, it becomes less hydrophobic and more lipophobic (fat hating), so it's much harder to moisturize or condition it with oils, fatty conditioning agents like behetrimonium methosulfate, and other oil soluble ingredients. The increase in pH and damage is permanent.
 
While we might be able to use well-formulated alkaline products on our skin, our hair is all about the acidic ones. If you’ve used an alkaline soap on your hair, you’ve likely felt the impact a higher pH cleanser can have with a scratchy or straw-like feeling after rinsing thanks to the lifted cuticle. We can use alkaline relaxing and straightening products every once in a while, but even infrequent use could cause a lot of damage. Listen to your hairdresser’s advice and condition well after those kinds of treatments.
 
The biggest concern about pH in our handmade products arises when we start making surfactant based products like shampoo, body wash, or face cleanser. While most surfactants are acidic, the few that aren’t, like decyl glucoside, are the ones most likely to catch your eye when you’re looking for new and fun ingredients. As much as I love the gentle cleansing of decyl glucoside and the super cool amphoteric and mild nature of disodium cocoamphodiacetate, I only use them when I can test the final results with a good pH meter. It might be easier and less expensive to buy pH strips, but they simply aren’t accurate enough for crafting with surfactants and fruit acids, and it would be a waste of ingredients and energy to make something awesome only to find that it’s making our skin drier and our hair damaged.
 
What can we do if our product’s pH is out of whack or if we want to make a more acidic or basic product? To decrease the pH or make it more acidic, you can use a tiny bit of citric acid, glycolic acid, or AHAs. To increase the pH or make it more alkaline, you can use sodium hydroxide (diluted to 18%) or triethanolamine. Test your pH meter with a buffer solution – I like to try it with pH 4 and 10 every session – and ensure it’s measuring accurately. Add your acidic or alkaline ingredient by 0.05% to 0.10% to the finished product, measuring the pH after every addition. If you need to add more, go up by 0.05% increments and measure every time. You’ll need to follow this process with every batch because no two products are ever the same, and 0.10% might have been great last time, but too much now.
 
While I can’t speak for every recipe you might find out there, most formulations you’ll find on reliable sites and blogs will be pH balanced if you follow their recommendations for ingredients. If you want to start adding exciting cosmeceuticals or actives, check the pH ranges in which they’ll work and the final product to which you’ve added it. As well, double check the pH ranges for your preservative to make sure it’ll work at a lower or higher level. It’d be a pity to make a lovely product only to find out it’s causing more problems than it’s solving!