Apple Cider Vinegar for the Skin: The Importance of Maintaining an Acid Mantle

Apple cider vinegar (AVC) is an ancient remedy, noted by Hippocrates and the Babylonians for treatment of infection and wound healing, and produced commercially as far back as at least 5000 years ago (Yagnik et al., 2018). Simply-made, nutritive and healing, ACV is an excellent addition to your skincare regime for a couple of reasons. Its acidity supports our protective acid mantle, which we so habitually strip away with alkaline products and water, and its flavonoids and phenolic acids protect from the damaging effects of UV rays, pollution and other stressors our skin is bombarded with day after day.

What is the Acid Mantle?

In 1928, Dr. Alfred Marchionini coined the term the “acid mantle” to describe the thin acidic layer covering our outer skin cells (Schade & Marchionini, 1928). On the pH scale, a measure of acidity versus alkalinity, human skin is between pH 4.5 to 5.5, while neutral pH is 7 and alkaline substances are pH 7 to 14. This is in contrast to the nearly-neutral pH of the internal body (Elias, 2017). 

Why Skin is Acidic

The acid mantle is one of the body’s ways of protecting itself from microbial invaders. We’re all covered in countless microbes like bacteria, fungi and even viruses, but infectious species can’t thrive in acidic environments. Making the skin acidic prevents these microbes from proliferating. An acidic pH is also required for certain enzymes to produce ceramides that are critical in the skin’s barrier function, and for the skin to produce oils that protect it from dehydration. Finally, an acidic environment prevents other enzymes from breaking down skin proteins, which can lead to the premature death of skin cells (Ali & Yosipovitch, 2013).

How the Skin Produces Acids

It was previously thought that acids are produced as free fatty acids in the pores along with sebum, or the waxy oil that protects the skin from drying out. Now, we know that there are other mechanisms that produce acids in the skin (Elias, 2017). There are several theories about these other mechanisms, and an interesting one has to do with the melanin content of the skin. Melanin granules, which confer pigmentation to the skin, are acidic. Studies have shown that those with darker skin have lower pH and better barrier function and cohesion at junctions between skin cells than those with less melanin (Gunathilake et al., 2009).

Soap and Water are Alkaline

The pH of pure water is a neutral 7, with hard water or seawater having an alkaline pH of above 8 and soft water being about 6. On top of that, soap is inherently alkaline. Lye, an ingredient used to make natural soaps, is so alkaline that it will burn the skin if applied undiluted. The majority of soaps on the market have a pH above 9, and shampoos have a pH of 6-7 (Tarun, et al., 2014). 

What Happens When you use Alkaline vs Acidic Products

Soap and water are above the skin’s ideal pH of 4.5 to 5.5, meaning that applying them to the skin will disrupt its acid mantle. You may have experienced this after taking a swim or getting out of the shower, when your skin feels dry and tight if you don’t apply some kind of moisturizer. This is partly due to loss of sebum, but studies show that skin hydration is also affected by pH. One study had subjects use a low-pH (4.5) lotion on one arm, and regular (pH 6.5) lotion on the other, and found that the skin where the low-pH lotion was used was significantly more hydrated and skin barrier integrity (how well skin cells are connected to each other) was significantly better than the skin using the regular lotion. This correlated with a lower pH of the low-pH-treated skin (Blaak et al., 2020). 

This tells us a few things. 1. It’s not just loss of skin lipids that causes dryness, it’s also loss of acidity. 2. Using low-pH skin products reduces the pH of the skin over time (in this study, over four weeks). 3. The reduced pH isn’t confined to when the low-pH product is first applied (subjects didn’t use the lotions for 10-16 hours before testing). In summary, applying low-pH products supports our skin’s natural acid mantle over time, improving its hydration and health.

An Impaired Acid Mantle Causes Skin Infections

As acidity is a major antimicrobial defense of the skin, repeatedly stripping away this acid defense with alkaline products allows infectious microbes to grow. This could open the door to fungal infections like athlete’s foot, yeast infections and ringworm, or bacterial infections like Propionibacterium acnes, which causes acne, and Staphylococcus aureus, which contributes to, and may even cause, eczema (Baker et al., 2023). Alkaline pH could also contribute to antibiotic-resistance Staph infections (MRSA), as antibiotics against them don’t work as well in alkaline environments (Lemaire et al., 2007). 

An Impaired Acid Mantle Causes Skin Inflammation

Our commensal (helpful) skin microbes thrive in an acidic environment. They produce anti-inflammatory chemicals called IL-12 that reduce allergic reactions, while pathogenic microbes at higher pH trigger inflammation. Reduced acidity also allows an enzyme called serine protease to flourish, which causes inflammation, increases susceptibility to eczema and ultimately damages the structure of the skin (Baker et al., 2023). Inflammation is a root cause of cell damage, chronic disease and premature aging. The inflammatory process is meant to be a first line of defense against tissue damage and invading organisms, but it doesn’t differentiate between pathogens or damaged areas and our own healthy tissues. It’s sort of the shotgun defense of the immune system, spraying everything with damaging chemicals in order to deal with a problem. It creates a positive feedback loop: inflammation causes more damage, which initiates more inflammation. Without an outside intervention, inflammation can run amok, damaging and aging the skin.

An Impaired Acid Mantle Decreases Ceramides

Other enzymes that thrive at a lower pH are beneficial to skin’s hydration, upregulating ceramides, the main lipids that prevent dehydration and retain water inside the skin. High pH upregulates alkaline ceramidase, which breaks down ceramides, leading to barrier lipid degradation and loss of skin moisture. In addition to retaining water in the skin, ceramides promote a process that eliminates abnormal mitochondria. Mitochondria are the cell’s power plants, producing the energy needed to pump out acid and maintain the acid mantle of the skin. Thus, stripping away the acid mantle triggers a chain reaction that reduces ceramides, further reducing acid production in the skin (Baker et al., 2023). 

An Impaired Acid Mantle Causes Allergies

Ceramides also produce IL-12, which reduces allergic inflammation. Interestingly, scientists are finding that developing allergies is highly related to skin health. Skin barrier abnormalities allow penetration of allergens, predisposing patients to the common trifecta of eczema, asthma and environmental allergies. Studies show that applying products that acidify the skin prevent development of eczema, or flare-ups if it’s already present, and prevent the progression of eczema to allergen-triggered asthma in animal models (Lee et al., 2017). With reduced skin acidity, the barrier is compromised and pathogenic microbes like Staph are allowed to flourish, causing eczema and inflammation. This type of inflammation leads to activation of antibodies, which are responsible for allergic reactions. Over time, the antibody response starts to attack environmental allergens, making the skin more sensitive and causing allergic rhinitis, asthma and food allergies and intolerances (Baker et al, 2023). 

Apple Cider Vinegar for Restoring the Acid Mantle

ACV is made from fermentation of raw apples by yeasts, which first make alcoholic apple cider, and acetic acid bacteria, which transform the alcohol to acetic acid. The end product is 5% acetic acid, with a pH of about 3-4. Acetic acid bacteria may remain in the final product and can form a harmless dark cloud in the vinegar, called the “mother.” Studies show that ACV is rich in antioxidant, anti-inflammatory and antibacterial compounds such as phenolic acids, tannins, flavonoids and carotenoids (Kelebek et al., 2017). 

Researchers suspect that these health-promoting compounds may be responsible for ACV’s lipid and glucose-lowering abilities when taken internally (Hadi et al., 2021). In vitro research has found that ACV works as an antimicrobial against Candida albicans (the fungus that causes yeast infections, thrush and some types of athlete’s foot), Escherichia coli and Staph infections, including MRSA and antibiotic-resistant E. coli in lab cultures (Yagnik et al., 2018; Yagnik et al. 2021). It’s not clear if the phenolic acids, tannins, flavonoids and carotenoids play a role in its antimicrobial activity, with one study having equal antimicrobial effects using both ACV and plain acetic acid of the same pH, but noting that other studies using an ACV with a higher phenolic acids concentration displayed more effective antimicrobial properties (Chandraseharan et al., 2023). 

Studies do show that some of the known compounds in ACV have their own beneficial properties. ACV is highest in flavonoids, including quercetin, luteolin and phloridzin, and phenolic acids, including chlorogenic, vanillic and gallic acids (Kelebek et al., 2017). Quercetin is a strong antioxidant and anti-inflammatory, scavenging free radicals and quelling the inflammatory response (Tang et al., 2019). One in vitro study used human skin cells treated with the same pro-inflammatory chemicals found in eczema, with one sample pretreated with quercetin. The skin cells that were pretreated with quercetin showed significantly reduced expression of inflammatory chemicals and increased expression of powerful antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (Beken et al., 2020). Luteolin is shown to protect the skin against UVB sun damage. One animal study showed that skin with daily luteolin application had significantly reduced oxidative damage, increased collagen production and more available SOD after being exposed to UVB light, compared to controls (Mu et al, 2021). A final study showed that chlorogenic acid increases collagen expression, reduces free radicals and promotes cell repair in skin cells after UVA exposure (Xue et al., 2021).

What Happens When you Apply Apple Cider Vinegar to the Skin

Skin becomes softer, smoother and more hydrated immediately after applying ACV because of its pH-balancing properties. After exposure to water, especially with soap, the skin’s acid mantle is stripped away, leaving it exposed to dehydration, pathogenic microbes and inflammatory enzymes. Using ACV is a way to mimic and support the skin’s natural pH until the acid mantle has time to recover, alleviating stress on the skin and saving mitochondrial energy for other tasks like cell repair or regeneration. Acne and eczema are lessened or alleviated by creating an ideal environment for commensal microbes and a less-than-ideal landscape for P. acnes and S. aureus. The tightness or dryness that may be felt after coming out of the water is alleviated without moisturizer and the skin stays hydrated and dewy. The skin appears more youthful and healthy as its antioxidant power is maximized, reducing oxidative damage and strengthening collagen and skin cell cohesion. 

Check out Alimental’s Apple Cider Vinegar Facial Balancer.

References

Ali, S. M., & Yosipovitch, G. (2013). Skin pH: From basic science to basic skin care. Acta Dermato-Venereologica, 93(3), 261–267. https://doi.org/10.2340/00015555-1531

Baker, P., Huang, C., Radi, R., Moll, S. B., Jules, E., & Arbiser, J. L. (2023). Skin barrier function: The interplay of physical, chemical, and immunologic properties. Cells, 12(23), 2745. https://doi.org/10.3390/cells12232745

Beken, B., Serttas, R., Yazicioglu, M., Turkekul, K., & Erdogan, S. (2020). Quercetin Improves Inflammation, Oxidative Stress, and Impaired Wound Healing in Atopic Dermatitis Model of Human Keratinocytes. Pediatric allergy, immunology, and pulmonology, 33(2), 69–79. https://doi.org/10.1089/ped.2019.1137

Blaak, J., Theiss, C., Schleißinger, M., Simon, I., Schürer, N. Y., & Staib, P. (2020). A commercially available skin care lotion with a pH of 4.5 and 10% urea improves skin surface pH, stratum corneum hydration and epidermal barrier function in subjects with dry skin and atopic diathesis. Journal of Cosmetics, Dermatological Sciences and Applications, 10(3). doi: 10.4236/jcdsa.2020.103014

Chandraseharan, P., Sockalingam, S. N. M., Shafiei, Z., Zakaria, A. S. I., Mahyuddin, A., & Rahman, M. A. (2023). The Efficacy of Apple Cider Vinegar at Different pH Values as an Antimicrobial Agent: An In Vitro Study. The journal of contemporary dental practice, 24(10), 779–786. https://doi.org/10.5005/jp-journals-10024-3581

Elias P. M. (2017). The how, why and clinical importance of stratum corneum acidification. Experimental dermatology, 26(11), 999–1003. https://doi.org/10.1111/exd.13329

Gunathilake, R., Schurer, N. Y., Shoo, B. A., Celli, A., Hachem, J. P., Crumrine, D., Sirimanna, G., Feingold, K. R., Mauro, T. M., & Elias, P. M. (2009). pH-regulated mechanisms account for pigment-type differences in epidermal barrier function. The Journal of investigative dermatology, 129(7), 1719–1729. https://doi.org/10.1038/jid.2008.442

Hadi, A., Pourmasoumi, M., Najafgholizadeh, A., Clark, C. C. T., & Esmaillzadeh, A. (2021). The effect of apple cider vinegar on lipid profiles and glycemic parameters: a systematic review and meta-analysis of randomized clinical trials. BMC complementary medicine and therapies, 21(1), 179. https://doi.org/10.1186/s12906-021-03351-w

Kelebek, H., Kadiroğlu, P., Demircan, N.B., & Selli, S. (2017). Screening of bioactive components in grape and apple vinegars: Antioxidant and antimicrobial potential. J Inst Brew 123, 407–416. doi: 10.1002/jib.432.

Lee, H. J., Lee, N. R., Kim, B. K., Jung, M., Kim, D. H., Moniaga, C. S., Kabashima, K., & Choi, E. H. (2017). Acidification of stratum corneum prevents the progression from atopic dermatitis to respiratory allergy. Experimental dermatology, 26(1), 66–72. https://doi.org/10.1111/exd.13144

Lemaire, S., Van Bambeke, F., Mingeot-Leclercq, M. P., Glupczynski, Y., & Tulkens, P. M. (2007). Role of acidic pH in the susceptibility of intraphagocytic methicillin-resistant Staphylococcus aureus strains to meropenem and cloxacillin. Antimicrobial agents and chemotherapy, 51(5), 1627–1632. https://doi.org/10.1128/AAC.01192-06

Mu, J., Ma, H., Chen, H., Zhang, X., & Ye, M. (2021). Luteolin Prevents UVB-Induced Skin Photoaging Damage by Modulating SIRT3/ROS/MAPK Signaling: An in vitro and in vivo Studies. Frontiers in pharmacology, 12, 728261. https://doi.org/10.3389/fphar.2021.728261

Schade H. & Marchionini A. (1928). Der säuremantel der haut (nach gaskettenmessungen). Klin Wochenschr 7(1):12–14. doi: 10.1007/BF01711684

Tang, J., Diao, P., Shu, X., Li, L., & Xiong, L. (2019). Quercetin and Quercitrin Attenuates the Inflammatory Response and Oxidative Stress in LPS-Induced RAW264.7 Cells: In Vitro Assessment and a Theoretical Model. BioMed research international, 2019, 7039802. https://doi.org/10.1155/2019/7039802

Tarun, J., Susan, J., Suria, J., Susan, V. J., & Criton, S. (2014). Evaluation of pH of bathing soaps and shampoos for skin and hair care. Indian Journal of Dermatology, 59(5), 442–444. https://doi.org/10.4103/0019-5154.139861

Xue, N., Liu, Y., Jin, J., Ji, M., & Chen, X. (2022). Chlorogenic Acid Prevents UVA-Induced Skin Photoaging through Regulating Collagen Metabolism and Apoptosis in Human Dermal Fibroblasts. International journal of molecular sciences, 23(13), 6941. https://doi.org/10.3390/ijms23136941

Yagnik, D., Serafin, V., & Shah, A. J. (2018). Antimicrobial activity of apple cider vinegar against Escherichia coli, Staphylococcus aureus and Candida albicans; downregulating cytokine and microbial protein expression. Scientific reports, 8(1), 1732. https://doi.org/10.1038/s41598-017-18618-x

Yagnik, D., Ward, M., & Shah, A. J. (2021). Antibacterial apple cider vinegar eradicates methicillin resistant Staphylococcus aureus and resistant Escherichia coli. Scientific Reports, 11(1), 1854. https://doi.org/10.1038/s41598-020-78407-x