Australian-based chemistry PhD Michelle Wong launched her beauty blog Lab Muffin (@labmuffingbeautyscience) six years ago with one main mission: to give better explanations of the science behind beauty products. Her deep-dive commentaries of all things pH have become skin-care canon on Reddit—here, she answers our most burning questions.
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What is pH and how does it play a role in skin care?
“Short for ‘potential of hydrogen,’ pH is a numerical value usually ranging from zero to 14, identifying the acidity or alkalinity of a substance. In the world of skin care, alkaline cleansers like old-fashioned soap and shampoo have a high pH above 7, while alphahydroxy and salicylic acids typically have a low pH (3–4). Skin hovers between 4 and 6 and is protected from alkaline invaders and bad bacteria thanks to its ‘acid mantle,’ a potent (albeit kind of gross), low-pH film comprising sebum, sweat and dead skin cells. The products we apply can either throw off or stabilize our skin’s pH, but when it’s balanced, skin looks brighter and healthier.”
Which products are known to throw skin’s pH off balance?
“Traditional cleansers that contain surfactants such as sodium lauryl sulfate (SLS) are the biggest pH disruptors: A single cleanse with a strong soap can strip away the protective acid mantle and leave skin open to bacterial invasion. A classic study found that washing with a high-pH cleanser leads to an increase of acne-causing p-acnes bacteria on the skin, and after three months, test subjects had significantly more breakouts than when they started the protocol.
Surprisingly, even when using a pH-balanced cleanser, if the tap water used to rinse the skin afterward is high-pH—it can be tested using Litmus strips—it can still alter the skin. That’s why micellar waters—gentle cleansers that don’t need to be rinsed off—were created. But, micellar waters also contain surfactants—some are more irritating than others—so in my opinion, neither option is superior and it really comes down to personal preference.”
How do acid-based products affect the skin’s pH?
“Acidic topicals on the other end of the pH spectrum, such as vitamin C serums, chemical peels and alphahydroxy acid–based exfoliators, cause much less damage than alkaline ones. Acids are neutrally charged at a low pH, which lets them strip away dead skin, but not the acid mantle. They also tend to be more bio-available and penetrate skin more easily than their high-pH counterparts. But, layering too many acidic products can overexfoliate the skin and weaken its barrier, so moderation is key.”
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How effective are Litmus strips at testing pH?
“At-home pH-indicator strips are not always super precise, but they are accurate. I recommend using the type that have multiple indicator squares to narrow down the pH range and help identify any potential issues. For example, if one indicator reacts with something in the product in an unexpected way, you’ll still be able to get a pH range with the other indicators. Another tip is to dilute the product with a small quantity of water to make sure it soaks into the strip sufficiently. If it’s an emulsion, mix it with water thoroughly to break down the emulsion droplets as much as possible, and keep in mind that the pH may not be as accurate because aqueous droplets may not have completely broken up.”
What about acid toners…are they worth the hype?
“Many people use acid toners to lower the pH of their skin before applying low-pH products, but the low-pH product will drop their skin pH anyway. For that reason, I don’t think they’re a necessary step.”
What should someone do if their skin does become damaged?
“If skin does become damaged, everything from redness to dermatitis can result. Studies show some products affect the skin’s pH for up to six hours, but irritation can last for days afterward. One small study found that skin of color may not be affected in the same way as lighter skin tones because it may have a lower pH and stronger barrier. To help skin recalibrate, use products with pH-neutral and occlusive ingredients such as squalane and ceramides.”
What are your favorite pH-friendly skin-care products?
“I love low-pH alphahydroxy acid exfoliants like Paula’s Choice Skin Perfecting 8% AHA Gel ($29) and Pixi Beauty Glow Tonic ($29), and my favorite low-pH cleansers right now are Peter Thomas Roth Cucumber De-tox Foaming Cleanser ($35) and Krave Beauty Matcha Hemp Hydrating Cleanser ($16).”