Thursday, April 3, 2014

Beauty of Science #7: What is pH?

Remember these? The Beauty of Science posts are back, now that I am no longer writing a dissertation, ha (if you're new to the series, I'd start with one). We've covered sunscreens, oils, soaps. I'm always looking for topics, too, so feel free to send me some!

Today, though, I wanted to cover pH. Many products claim to personalize your shade based on your individual pH, and I thought I'd address that today.

In chemistry, pH = -log ([H+]). (Stay with me, guys). This simply means it's a measurement of the H+ (or proton) concentration of a solution - a measurement of how acidic or basic a solution is. What that means in practical terms, is shown below. pH runs on a scale from 0 - 14, with acidic solutions falling in the lower end of the scale, and basic solutions at the high end of the scale.

You'll see familiar items on the graphic: vinegar is acidic at pH ~2, water is neutral at 7, bleach is basic at ~13. Solutions at the extreme ends of the scale usually aren't great for humans to touch or consume (i.e., oven cleaner, pH ~13 or battery acid at pH 0) and biological functions generally flourish at near-neutral pH (i.e., ~7; for example, the pH of human blood is ~7.4).

Dikstein reports that the pH of skin ranges from 4-6 (thus called the "acidic mantle of skin" - also helps us sidestep the problem of skin being a solid rather than a solution...#chemistproblems); it differs between different areas of the body, and seems to be related to race and genetic background.[1]

What this means is, the skin pH of most people is going to fall within that range (healthy, alive people, that is). The pH of my skin? Probably from 4-6. The pH of your skin? Probably from 4-6. The idea of a "personalized product for your pH!" is therefore rather a stretch. (Incidentally, this is why straight up lemon juice as a facial treatment is considered damaging. It's pH ~2. Products that contain lemon juice as an ingredient probably have other items to balance out the pH - I am hoping! - so I don't write those off without further research).

Bonus: This great post at Of Faces and Fingers explains how the "color-changing" ingredients work; it's a worthwhile read and really informative.

1. S. Dikstein and A. Zlotogorski, Measurement of skin pH, Acta Dermato-Vereologica (Stockh) Suppl., 185, 18-20 (1994).

[If you are reading this on any other site besides Eye Heart It, it is stolen content and should be reported. Thank you!]