Skin pH Testing – A Useful Tool to Measure Microbiome Health?

Ben Eshelby, compounding pharmacist and cosmetic scientist, shares the findings from an exploratory study conducted to observe the skin pH of skin with different skin conditions.

Any avid gardener will attest that one of the most important properties of soil to ensure a healthy garden is the pH. Whilst plants are obviously of a different living kingdom to bacteria, similar principles exist between the propagation of a healthy garden and that of a healthy skin microbiome. 

It has been known for almost a century that the pH of healthy skin is acidic and that pathogenic bacteria appear to flourish on the skin as the skin becomes more alkaline^1,2. It is also understood that commensal bacteria on the skin are responsible for breaking down lipids in sebum and creating free fatty acids – making their own acidic environment and supporting their own growth.  On this basis, it could be suggested that the pH of the skin could be used as a rough indicator of microbiome health.

Study on skin pH and skin conditions

Hypothesis

The pH of healthy skin has been traditionally placed anywhere between 4-7, but newer studies are starting to suggest that an ideal pH is somewhere below 5^3,4. Thus, we decided to explore the utility of using skin pH testing as a means of identifying microbiome health and observed the pH of skin from those that had been clinically diagnosed with acne, rosacea, and eczema, and those whose skin had no established pathological skin condition.

Data selection

Data was gathered from a large database of thousands of clients who had received a skin consultation prior to having personalised skincare made from a compounding pharmacy. As part of the consultation process, the pH of the skin was taken on the cheek using a digital pH meter with a flat base designed for skin measurements. Hydration, sebum content, and pore size were also examined using UV analysis. 

The data was then divided into several different groups depending on the nature for which the client required skincare: cosmetic, acne, eczema or rosacea. It should be noted that those with acne, rosacea and eczema had all been previously diagnosed by a physician. The cosmetic group was assigned to clients who had no disorders of the skin per se but wished to use skincare products to enhance the health of their skin.

To obtain a suitable sample size, the database was scanned alphabetically and the data of the first 25 people that could be placed in each of these groups was selected. A small sample was chosen to make a concise observation of a larger, more comprehensive study currently being conducted. Data where clients had previously used acidified, prebiotic skincare from the pharmacy, and so were likely to have altered skin pH from these products, were excluded.

The results

The measured pH values of skin in the four groups are as follows:

The cosmetic group had the lowest mean pH of 5.14 with a range between pH 4.25 and 6.05. . Those suffering from rosacea had a mean skin pH of 5.83 with a pH range between 4.98 and 6.65. The acne group had a mean pH of 6.06 and a pH range from 5.01 to 6.85. Those with eczema had the highest mean pH of 6.27 and a range from pH 4.71 to 6.74. The mean of all four groups was 5.82 which is significantly higher than the study

What do the findings tell us?

Cosmetic
Clients without any notable pathological skin conditions – the cosmetic group – had a skin pH above 5 which, as mentioned above, could be considered less than ideal.  From a cosmetic perspective it is interesting to note that whilst these clients had no diagnosable skin condition, they were all seeking to improve the appearance of their skin. 

A raised pH has been associated with decreased hydration levels of the skin⁵. Visually, dehydrated skin is dull and signs of ageing such as wrinkles and dark circles are more apparent.

Rosacea

Previous studies have recognised changes in pH in those with rosacea. The relationship between demodex mites, the microbiome and rosacea has been frequently discussed but is still not well understood. A Turkish study conducted in 2017 found greater numbers of demodex mites in skin with higher pH values but this was not statistically significant so definite conclusions could not be drawn⁶. Another study looking at papulopustular rosacea in particular noted a significant increase in skin pH so there may be type-specific changes in pH ⁷. However, we did not differentiate between different types of rosacea in our observations so cannot attribute the higher values observed to a specific type. Characterisation of rosacea, such as low hydration that evidences a damaged skin barrier function, is indicative of microbial dysbiosis. The average pH of 5.83 we found is higher than the suggested optimal level of below 5. This supports the notion the microbiome was somewhat compromised.  Further research looking at treating rosacea or preventing recurrent flareups by repairing the microbiome, accounting for pH, would be needed to draw further conclusions and could yield interesting results.  

Acne

Acne is often associated with particular strains of C. acnes bacteria, which tend to flourish in an environment in the range of pH 6-6.5 and tends not to favour a pH of less than 5.5⁸. Furthermore, it has been reported that a pH of below 4.5 may be bactericidal to C. acnes⁹. Evidence suggests that the increase in pH seen in skin with acne is due to an increase in sebum with a decreased free fatty acid content¹⁰. Our findings of an average pH of 6.06 for those suffering with acne aligns with this. It could be concluded that when looking at skincare for people suffering with acne, pH is critical but also the type of lipid used. Perhaps by enrichening the skin artificially with natural oils dense in free fatty acids, a healthy microbiome may be restored.

Eczema

Eczema is characterised by decreased hydration, altered skin barrier function, and increased pH which indicates an imbalance of skin micro-organisms. It is well known that there is also commonly an abundance of S. aureus associated with the condition. S. aureus has been shown to grow most rapidly at a pH of between 6-7¹¹. Our skin pH testing supported this, with an average pH of 6.27 being found.

Summary

Common to all the pathogenic skin conditions we looked at was a raised pH. The raised pH we found corresponded to other findings in the literature and supported theories of dysbiosis. Interestingly, the sample we looked at where no skin conditions were present had an average pH higher than what has been suggested to be ideal. This group whilst having no obvious skin maladies, were seeking something for their skin to make it look better, suggesting that raised pH of the skin above pH 5 may accentuate the visible signs of ageing. This has implications for formulators in the cosmetic industry.

Restoring a well-balanced microbiome in all these groups could be achieved by artificially creating an ideal environment for commensal bacteria. Using the gardening metaphor above, to make a garden healthy, one needs to add nutrients (or free fatty acid rich lipids), correct the pH, and ensure there is minimal chemical harm done to the living organisms in the soil (minimal preservation) – which in this case is the human skin. The testing of pH of the skin could be useful in determining the health of the microbiome and preparing suitable products for skin conditions. It could also be a useful tool to quantitatively measure the success of skincare treatments.

While the link between pH and microbiome dysbiosis still needs to be fully established, the pH remains an important axis to explore. Indeed, the potential of modulating skin conditions through the microbiome and pH levels is enormous. With new research into the pH of the skin and information gathered from technology such as the wearable pH device by L’Oreal¹², it may not be long before a solid link between pH and microbiome health is established. 

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References

1. Schade H, Marchionini A. Der sauremantel der haut. Klin Wochenschr. 1928 7:12-14.
2. Marchionini A, Hausknecht W: Sauremantel der haut und bakterienabwehr. Sauremantel Haut Bakterienabwehr. 1938. 17:663-666.
3. Segger D, Assmus U, Brock M, Erasmy J, Finkel P, Fitzner A, et al. Multicenter study on measurement of the natural pH of the skin surface. Int J Cosmet Sci 2008;30:75.
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5. Elias, P.M. Stratum corneum acidification: how and why? Exp. Dermatol. 2015; 24:179– 180.
6. Zeytun, E., Tilki, E., Doğan, S., & Mumcuoğlu, K. The effect of skin moisture, pH, and temperature on the density of Demodex folliculorum and Demodex brevis (Acari: Demodicidae) in students and staff of the Erzincan University, Turkey. International Journal of Dermatology. 2017; 56(7):762-766.
7. Ní Raghallaigh, S., and F.C. Powell. Epidermal hydration levels in patients with rosacea improve after minocycline therapy. British Journal of Dermatology 2014;171(2): 259-266.
8. Korting HC, Lukacs A, Vogt N, Urban J, Ehret W, Ruckdeschel G: Influence of the pH-value on the growth of Staphylococcus epidermidis, Staphylococcus aureus and Propionibacterium acnes in continuous culture. Zentralbl Hyg Umweltmed 1992;193:78–90.
9. Valle-González, Elba R., Joshua A. Jackman, Bo Kyeong Yoon, Natalia Mokrzecka, and Nam-Joon Cho. pH-Dependent Antibacterial Activity of Glycolic Acid: Implications for Anti-Acne Formulations. Scientific Reports 2020; 10(1).
10. Pappas A, Johnsen S, Liu JC, Eisinger M. Sebum analysis of individuals with and without acne. Dermatoendocrinol. 2009;1(3):157–161.
11. Korting HC, Lukacs A, Vogt N, Urban J, Ehret W, Ruckdeschel G. Influence of the pH-value on the growth of Staphylococcus epidermidis, Staphylococcus aureus and Propionibacterium acnes in continuous culture. Zentralbl Hyg Umweltmed. 1992 Jun;193(1):78-90.
12. L’Oreal unveils prototype of first-ever wearable microfluidic sensor to measure skin pH level. L’Oreal Finance Website. Published 7/1/19, Accessed 1/3/2021. https://www.loreal-finance.com/eng/news-event/loreal-unveils-prototype-first-ever-wearable-microfluidic-sensor-measure-skin-ph-levels