The pH of your skin and skincare: Ten Q and As
1. What is pH?
It’s a measure of the acidity of water-based solutions (you can’t measure pH in an oil!). There are strong acids like sulfuric acid (pH will be very low even at low concentrations) and weak acids, like ascorbic acid, that will keep pH below 7 but not too low.
2. What is that pH number?
pH is a scale that specifies the acidity or basicity of an aqueous solution. Acidic solutions (solutions with higher concentrations of H+ ions) are measured to have lower pH values than basic (a.k.a. alkaline) solutions. The pH scale is logarithmic and inversely indicates the concentration of hydrogen ions in the solution. High proton concentrations, low pH. Low proton concentrations, high pH.
3. Why does lemon juice taste sour?
Lemon juice tastes sour because it contains 5% to 6% citric acid and has a pH of 2.2 (high acidity). This is a very low pH, but gastric juice is even lower, about 1 to 1.5; this means that protons are ten times as concentrated in the stomach as in lemon juice.
4. Give me examples of alkaline pH
Ammonia, approx. 11; lye, 13 or higher.
5. Should you worry about your skin’s pH?
No, unless you are messing up with it. Your skin self-regulates, so unless you disturb your skin with unphysiological procedures or products, its pH will stay stable at about 5 to 6.
6. What is the acid mantle?
The acid mantle is an old name that expressed the belief that epidermal pH was important to skin physiology (they were right!). It does not reflect a physical location.
7. Does the skin’s pH vary a lot?
Not really, unless you take a long bubble bath.
8. What’s wrong with increasing skin pH? Bad for bacteria is good for me, right?
No! Increasing your skin’s pH will kick out good bacteria and invite fungi, which is a bad idea.
9. Do you need to measure your skin’s pH? How?
It’s not that easy; pH is a property of water-based solutions, so the existing measuring systems (including pH paper, pH meters) are designed for solutions, not to apply on the skin. Whatever you measure, it will be misleading. Leave your skin alone!
10. Should you measure the pH of your skincare products?
Again, it’s not easy unless you measure a water-based serum’s pH.
Some skin care products shout their “bad ph”. Like “natural antiperspirants, no need to measure pH when they contain bicarbonate and their objective is to increase skin pH.
Some interesting facts
Skin pH is affected by many endogenous factors, like skin moisture, sweat, sebum, anatomic site, genetics, and age.
Exogenous factors like detergents, application of cosmetic products, occlusive dressings, and topical medicines may influence skin pH.
Changes in the pH play a role in skin diseases like irritant contact dermatitis, atopic dermatitis, ichthyosis, acne vulgaris, and Candida albicans infections.
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Lambers, H.; Piessens, S.; Bloem, A.; Pronk, H.; Finkel, P. (2006). Natural skin surface pH is on average below 5, which is beneficial for its resident flora” International Journal of Cosmetic Science. 28: 359–370. doi:10.1111/j.1467-2494.2006.00344.x
Surber C, Humbert P, Abels C, Maibach H. The Acid Mantle: A Myth or an Essential Part of Skin Health? Curr Probl Dermatol. 2018;54:1-10. doi: 10.1159/000489512. Epub 2018 Aug 20. PMID: 30125885.