How pH Affects the Skin
About the author: Dr. Hanan Taha, M.D. is a Contributing Writer to FutureDerm.com. Dr. Taha received her MD from Kuwait University in 2002, and a master’s degree in Dermatology from the University of Alexandria in 2010. She also runs a blog in Arabic dedicated to spreading the knowledge about dermatology and cosmetic dermatology in a simple, concise manner (elbashra.com). For her full bio, please visit our About page.
A week ago, in my article about Dark Knuckles, I advised against using pure lemon juice directly on your skin. Half way through the week though, Nicki mentioned grapefruit as one of the ingredients in one of her favorite products, LUSH Ocean Salt Scrub. But wait, grapefruit is also acidic, what gives? The simple answer is, well, the grapefruit in LUSH Ocean Salt Scrub is not pure fruit juice as the lemon juice you squeeze at home. So it’s pretty obvious, but let’s dive a little bit more into pH in relation to the skin.
WHAT is “pH” anyway?
“Potential Hydrogen”: is a measure of acidity or alkalinity of a solution on a scale from 0 to 14, with 7 representing neutrality. Anything below 7 is acidic, anything above is alkaline. The further away you are from 7, the stronger the alkalinity or acidity of the solution is. An example of a very strong acid is sulfuric acid, and an example of a very strong alkali is lye (sodium hydroxide).
The Skin’s Normal pH
Normal skin pH ranges from 4.5 to 6.5, which means it is always on the slightly acidic side. This acidity of the skin is termed the “acid mantle” and is maintained by sebaceous glands, sweat glands, normal skin flora, among others.(1) It serves many protective functions to the skin, one of which is killing unwanted bacteria.(1) It has even been found that people suffering from acne have a slightly higher skin pH, and that bringing it down helps control acne.(2)
What happens upon applying something alkaline or acidic to the skin?
In either case the pH is affected.
If it is alkaline (or neutral): the stratum corneum (uppermost layer of the skin) is disrupted, damaging the barrier function of the skin, which translates into skin dryness and decreased antibacterial defense. A study has shown that using a skin cleanser that is basic – alkaline – like regular soap, can cause this kind of damage even after one use, and the effect is cumulative, meaning it gets worse with repeated use. These effects will of course be more pronounced in people suffering from dermatitis, people who have sensitive skin, and in the elderly, as this subgroup already has some damage going on, and their skin’s ability to fight these assaults is suboptimal.(3)
As for acids: here is where it gets a little bit tricky. The skin as we said leans more towards the slightly acidic side. Applying a mildly acidic product actually soothes the skin, helping it retain moisture and strengthening the skin barrier even more.(4) But there is a catch: how low can you go! Let’s take citrus fruits as an example.
Citrus fruits have many advantages, whether ingested or applied topically. They’re aromatic, they’re antibacterial, they’re a good source of vitamin C, they’re full of fibers, etc.
I’m Confused. So what’s so bad about pure lemon juice or grapefruit juice or any kind of citrus fruit juice for that matter?
Lemons – not for the skin!
Citric acid is one of the alpha hydroxy acids, or fruit acids: a group that also contains glycolic acid and lactic acid. They are used as skin peels. They exfoliate the skin and help bring youth back to sun damaged and aged skin.
Citrus fruit juice has a pH of about 2-3, and that makes it likely to cause things such as: skin irritation, sun sensitivity, and skin hyperpigmentation. Citric acid is found in citrus fruits at a concentration of about 5-10%, high enough to possibly lead to these side effects, especially in sensitive or broken skin. You’re basically using a mild superficial peel on your skin.
Another point to take into account when considering actual grapefruit or lemon juice is their water content. YES, applying water to your skin WILL dry it out. How? These fruits are made of 80% or more water, but contain NO occlusive ingredients. So when you apply lemon juice on your skin and let it air dry, you’ll end up with even drier skin after it evaporates.
Yes, lemon or grapefruit have citric acid, an alpha hydroxy acid that is beneficial to the skin. But consider 3 things:
1- The amount of time you leave it on your skin.
2- Its concentration: a little acidity is good for the skin, but stronger acidity turns the product into a peeling agent. That’s when you need to be careful. That said, there are many recipes out there that combine lemon juice with other products for the purpose of brightening the skin. Those I have nothing against, as long as the other ingredients are also healthy. This is, in effect, brining down the acidity (or brining up the pH) of the lemon juice, which would make it milder.
3- Note that, as Lush themselves advice on their website, if you have sensitive, dry skin, you might want to try some of their gentler scrubs.
Side note: contact with very strong acidic or alkaline products causes chemical burns. However, as we are discussing the pH of skin care products, chemical burns are outside the scope of this article and thus were not discussed.
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1- W. Joachim et al. Stratum corneum pH: Formation and Function of the Acid Mantle. Exogenous Dermatology 2002; 1(4):163-75.
2- N. Schurer, M. Bock. Lowering Lesional Surface pH in Acne: A New Treatment Modality for Herpifix. Journal of Dermatological Treatment 2009; 20(1): 27-31.
3- L. Baranda et al. Correlation between pH and Irritant Effect of Cleansers Marketed for Dry Skin. International Journal of Dermatology 2002; 42: 494-9.
4- E. Kim et al. The Alkaline pH Adapted Skin Barrier is Disrupted Severely by SLS Induced Irritation. International Journal of Cosmetic Science 2009; 31: 263-9.
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