Friday, March 8, 2013
Chemistry Thursday on Friday: Let's take a look at pH
Our skin is somewhere between 4.5 and 5.5, but it can vary based on location, gender, age, climate, and a ton of other things including the use of cosmetics and tap water.
Someone recently commented that it makes more sense to use an alkaline product on our skin, not an acidic product. This would make sense if you were trying to neutralize the acid, but we aren't trying to neutralize the pH of our skin to 7. Using an alkaline product will result in misery from the consequences I list above. This is not my opinion; it is based upon the studies I have quoted in the linked post above and the ones after it. If you you think you should be using alkaline leave on products on your skin, try this experiment. Make any product and add 0.5 grams of 18% sodium hydroxide (18 grams sodium hydroxide into 82 grams of water) or tetrasodium EDTA at 0.1% for every 100 grams of product until you reach an alkaline level of 8.5 or higher. Use this product every day for a week. You will see that our skin really doesn't like alkaline products left on our skin. As a disclaimer: Please don't try this. It will end in misery.
Let's take a look at a little experiment I did in the workshop that resulted in some neat pH stuff! I wanted to make a 3-in-1 shampoo, conditioner, and body wash for after swimming for my husband and me. I read that chelating ingredients like citric acid and EDTA can help bind the metals from the pool, so I thought I'd give this a shot. I know the tetrasodium EDTA is quite basic - 10.5 to 12.5 at 1% in water - and citric acid is acidic - about 3 or so - so I thought I'd see what they did in water.
I measured out 80 grams of reverse osmosis water that had a pH of 6.6 and added 0.4 grams of EDTA (works out to 0.5% EDTA). It jumped to 10.59 in a few seconds!
Wow! Let's make this more acidic by adding 0.4 grams citric acid (again, 0.5% citric acid). It plummeted to pH 4.44.
Wow! How cool is that? And it really makes it very clear that adding a tiny bit of a very alkaline thing - EDTA - or acidic thing - citric acid - is something to take seriously. But we don't tend to make products that are just water and some lye, so how does the inclusion of other ingredients affect pH?
I created my product with 0.1% citric acid and 0.1% EDTA, and it was well balanced at pH 5.88 in the end.
So what does this all mean? Be aware of the pH of your products. There are products - especially those with AHAs, BHAs (salicylic acid), or certain cosmeceuticals that need to be a specific pH to work. And there are preservatives that can only work in certain pH ranges. Check your ingredients before you start messing about with them!
As a note, I make sure the recipes on this blog are pH balanced. If you substitute an ingredient that has a really high or really low pH, you might want to test the product to ensure you're at the right level. But I try to worry about that for you - I am not the biggest fan of pH strips, and who amongst us owns a pH meter? (My chemistry professor didn't even have one!)
I just bought some phenolphthalein from Voyageur Soap & Candle, and we are going to have fun with that in a few weeks! The more alkaline the liquid, the pinker the colour, the more alkaline it is. It's easy to figure out which is the most alkaline liquid in the picture above.
Join me Monday for that 3-in-1 swimming product! No guarantees it works, but it smells like chocolate, which is awesome!
A few thoughts about the pH of our skin
Adjusting pH in our products