There’s a question I’ve been avoiding:
Does the alkaline pH of Dr. Bronner’s soaps interfere with the acidic pH of the skin’s acid mantle?
It keeps finding me. I knew what answering this would take. I knew that sifting through the hype, marketing, and misinformation surrounding the concepts of the acid mantle, pH balance, and soaps vs. detergents would take a lot of research and a whole lot of time. I was right.
Through the years, I’ve given somewhat glib answers to readers’ questions, mostly along the lines of “don’t worry about it.” I do apologize. Though for the most part, that was – and still is – true, it is hardly a satisfactory answer. In part, I was lazy. In part, I didn’t have the time. In part, I was scared my family’s soap would come up short.
Spoiler alert – it didn’t. I shouldn’t have doubted.
In the spirit of “taking more time to write less” I have extracted the key points from the 17 pages of notes I compiled from reading 40+ studies. You’re welcome. I must admit – once I dove in, it was kind of fun – in a nerdy, geeked-out sort of way. There were times as I read through the research that I yelped for joy. You think I’m kidding?
Now it’s your turn to learn.
Cast your mind back to 8th grade science when you dipped those little strips of litmus paper into various liquids and the strips instantly turned yellow or purple. That was pH in action. pH stands for “potential Hydrogen” and indicates acidity or alkalinity. Coffee is acidic. Cabbage is alkaline. Water is neutral. After the initial “oohs” and “aahs”, maybe you haven’t thought about it since, but pH is all around you.
Everything that’s water-soluble has pH, measured on a scale from 1 to 14. A neutral pH is in the middle at 7; acids are below 7, and alkalis above 7. Any extreme of pH – towards 1 or 14 – can eat through our skin. Sometimes acids and alkalis react. Think of those baking soda (alkali) & vinegar (acid) volcanoes you made in that same 8th grade science class.
The Acid Mantle
The acid mantle is a film over our bodies, produced in part by our outermost layer of skin, the Stratum Corneum, and in part by the bacteria that live on our skin. (Now don’t get grossed out by the thought of that bacteria – you need it. It’s your friend.) The acid mantle protects the skin from dehydration, infection, and environmental stressors like wind and grit. To build the acid mantle, the Stratum Corneum contributes sebum (oils, waxes, esters) and sweat (water, salt). The acidity develops when the bacteria on your skin break down the oils into fatty acids and glycerol. The pH of the acid mantle ranges from 5.0 to 5.5.[i]
The pH of Skin Cleansers
When it comes to skin cleansers, there are two categories: natural soaps and synthetic detergents. Soap has been around for millennia, the simple salt of a fatty acid, made by a one step reaction between an animal fat or plant oil and a strong alkali. Soaps are always alkaline. Milder soaps have a pH around 8-10, while harsher soaps can soar as high as 13. Synthetic detergents, developed in the last century, are derived from more complex reactions based on petroleum or plant oils. They are usually neutral to acidic in their pH.
What this means for Dr. Bronner’s…
Dr. Bronner’s soaps are true soaps made from organic coconut, palm kernel, olive, hemp, and jojoba oils. Because of our careful processes (more below), the pH of the Pure-Castile Liquid Soap is 9.3 ± 0.6, and the Pure-Castile Bar Soap is 9.8 ± 0.3, which are very mild. The Organic Sugar Soaps and Organic Shaving Soaps, due to the Shikakai powder, have the even more exceedingly mild pH of 8.5 ± 0.5.
The Impact of Cleansers on the Acid Mantle
Both soap and detergents impact the acid mantle during cleansing.[ii] Both types of cleansers work in the same way – binding oil to water in a magical process called emulsification. (What a great word!) This means that on our skin, these cleansers are attracted to the oils. This process removes the oils, sweat, bacteria, and odors our body has emitted, as well as any external oils, dirt, bacteria, and grime that has stuck to our skin. Unless we forego washing (which is culturally and hygienically questionable) or wash less (which has some merit in certain cases), the acid mantle is going to get disrupted regularly. But it was built to withstand it. Nonetheless, we need to clean ourselves with as little disruption as possible to the acid mantle and help our skin replenish.
The Concern of Skin pH and Soap
Although cleansing does disrupt the pH of the acid mantle, this disruption is not because of the pH of the cleanser. There is no acid/base reaction like the aforementioned baking soda/vinegar volcano. All cleansers, regardless of their pH, disrupt the pH of the acid mantle – be it an acidic detergent, an alkaline soap, or even neutral water by itself.[iii],[iv] This is because the cleanser is removing some of the acid mantle. Happily, though, the acid mantle is in a constant state of regeneration and returns to its normal pH within 30-90 minutes. The temporary pH disruption is not a concern.[v] Even long-term use of soap does not impact the pH of the acid mantle.[vi]
The Import of pH for Skin Cleansing
To sum it up, pH matters a bit, but not much. As long as you avoid an extreme pH, the skin easily accommodates being washed. In other words, avoiding the extremes, pH does not determine whether a cleanser is good for the skin.[vii] This is a well-documented conclusion, which is drawn in at least 11 distinct studies.[viii] There are more important things to consider in choosing a good cleanser.[ix]
What Makes a Good Cleanser?
Healthy ingredients, for starters.
Regardless what the front of a bottle says about itself, turn the bottle over and read the ingredient list. For help deciphering them, run the list through the Environmental Working Group’s Skin Deep Database to get their hazard rating on it. Look for these red-flags: sodium laureth sulfate, often contaminated by the carcinogenic 1,4-Dioxane;[x] Quaternary compounds, asthmagens that release formaldehyde, another known carcinogen; “Fragrance,” which is a category, not an ingredient, can hide phthalates, linked to reproductive harm as well as a jaw-dropping slew of other maladies.[xi] Problematic preservatives include parabens, which are hormone disruptors, and methylisothiazolinone, a skin irritant. Instead look for ingredients close to nature that receive low hazard ratings from EWG’s database. It also helps if a product has fewer ingredients. You then have less to monitor.
What this means for Dr. Bronner’s…
All Dr. Bronner’s products state a full list of their ingredients clearly on the label. The ingredients are selected to be the healthiest and best for our skin. No cheap shortcuts. The products are all plant based. No synthetics, no petrochemicals, no GMOs. Certified organic ingredients ensure product purity. Any scents are from pure essential oils. No artificial fragrances, no colorants.
Mildness is another factor that is more important than pH for maintaining a strong acid mantle and healthy skin. Surfactants, which is a word that describes both soap and detergents, have a tricky job. They are supposed to pick up oils, but how are they to know which oils to take away and which to leave behind? An aggressive surfactant strips out too many oils, even extracting oils below the acid mantle, out of the skin itself, causing irritation.[xii] Leave these cleaners for the dishes, where we want every oil gone. A mild surfactant takes only the readily available oils that are more loosely available on the surface of our skin.
The mildness of a cleanser depends on the size of its molecules. Not that I expect you to have a molecular microscope in your back pocket to see this, but let’s imagine for a moment. Smaller molecules can wiggle their way between skin cells, and have a stronger pull on oils, with the undesirable effect of extracting too many oils out of the skin. [xiii] Larger molecules can’t fit between those skin cells and so leave those oils in place.[xiv] There’s a balance to be found here, though. If a surfactant molecule is too large, it is less water soluble, meaning it doesn’t rinse off well. The size of a soap molecule depends on the length of its “tail,” which is a fatty acid chain. The length of a fatty acid depends on its number of carbon atoms. Soap molecules containing medium-long chain fatty acids (between 12 and 18 carbon atoms) strike this balance perfectly. [xv]
What this means for Dr. Bronner’s…
Fatty acids of this medium-long size are the primary types found in coconut, palm kernel, olive, hemp, and jojoba oils. [xvi] Dr. Bronner’s soaps are made with this perfect blend of oils, making the Pure-Castile and Organic Sugar & Shave Soaps superbly mild. Additionally, Dr. Bronner’s soaps are “superfatted.” This means, in the liquid Castile, Sugar, and Shave Soaps, that after the main soapmaking reaction has finished, a measured amount of citric acid is added to lower the pH and draw out some of the fatty acids. These free fatty acids increase the soap’s mildness, as well as contribute to a creamier lather and smoother feel on the skin. In the Castile Bar Soap, superfatting happens when the hemp and jojoba oils are withheld from the saponification reaction and are added afterwards. As I’ll explain below, these two oils have exceptional skin benefits.
Three More Ways to Strengthen the Acid Mantle
In addition to minimizing disruption by using mild surfactants, cleansers can further strengthen the acid mantle by incorporating three moisturizing components: occlusives, humectants, and emollients. [xvii] Pull those whoppers out at your next cocktail party! The word nerd inside me is jumping for joy. These three categories aid the skin in unique ways.
Occlusives lie on top of the skin and serve as a substitute acid mantle. Like the acid mantle, they protect against dehydration, infection, and environmental damage, and give the two other types of moisturizers a chance to do their part. Among plant-based ingredients that do this are almond, jojoba, soybean, and avocado oils.[xviii]
Humectants draw moisture back into the skin and work best beneath the protection of an occlusive. Among plant-based ingredients that do this are glycerin[xix] and various sugars, including honey and sucrose.[xx]
Emollients fill in the cracks between skin flakes, replacing lost lipids.[xxi] There are two fatty acids that do this particularly well: linoleic and alpha-linoleic fatty acids, neither of which can the body produce on its own. [xxii] They are readily found in a wide variety nuts, seeds, and leafy vegetables including safflower, wheat germ, sunflower, and hemp oils.[xxiii]
The skin benefits most when all three of these types of moisturizers are present together.
What this means for Dr. Bronners…
All of Dr. Bronner’s soaps contain jojoba oil (an occlusive), glycerin (a humectant), and hemp oil (a concentrated source of linoleic acid, an emollient).[xxiv] This means that the Liquid and Bar Castile, as well as the Organic Sugar & Shave Soaps supply what our skin needs to be strong and healthy. The Organic Sugar & Shave Soaps contain additional humectants, sucrose (sugar) and white grape juice, resulting in an even more nourishing cleanser.
When I began this self-directed course on pH and skin health, I wanted solid, peer-reviewed, unbiased research. No marketing campaigns. No hype. No trends. No celebrity commentary. I have never researched more than I have for this article. Possibly not even in college. I’ve included many references below for those who cry, “Show me the research!” You are my people, and that is our song. Needless to say, I’m glad to learn that pH of cleansers is almost a non-issue, and that my family’s formulations are well-founded. Though I’ve always thought that, it’s good to know why.
Special thanks to Dr. Vartan Libaridian, Dr. Bronner’s chemistry and R&D consultant, who breaks down the complexities of chemistry into phrases non-chemists can understand, and answered innumerable questions throughout my writing this article.
[i] Oranges, T., Dini, V., & Romanelli, M. (2015). Skin Physiology of the Neonate and Infant: Clinical Implications. Advances in wound care, 4(10), 587-595
[ii] DYKES, P. (1998). Surfactants and the skin. International Journal of Cosmetic Science, 20(1)
[iii] Gfatter R, Hackl P, Braun F: Effects of soap and detergents on skin surface pH, stratum corneum hydration and fat content in infants. Dermatology 1997; 195: 258–262
[iv] Bornkessel, A., Flach, M., Arens‐Corell, M., Elsner, P. and Fluhr, J. W. (2005), Functional assessment of a washing emulsion for sensitive skin: mild impairment of stratum corneum hydration, pH, barrier function, lipid content, integrity and cohesion in a controlled washing test. Skin Research and Technology, 11: 53-60. doi:10.1111/j.1600-0846.2005.00091.x
[v] Bechor R, Zlotogorski A, Dikstein S. Effect of soaps and detergents on the pH and casual lipid levels of the skin surface. J Appl Cosmetol 1988; 6:123-128
[vi] Takagi, Yutaka & Kaneda, K & Miyaki, M & Matsuo, K & Kawada, H & Hosokawa, H. (2014). The long-term use of soap does not affect the pH-maintenance mechanism of human skin. Skin Research and Technology. 21. doi:10.1111/srt.12170
[vii] Mark Oestreicher. Detergents. bath preparations, and other skin cleansers. Clinics in Dermatology 1998; 6:29-36
[viii] Ertel, Keith. (2000). Modern skin cleansers. Dermatologic clinics. 18. 561-75. 10.1016/S0733-8635(05)70207-2
[ix] DYKES, P. (1998). Surfactants and the skin. International Journal of Cosmetic Science, 20(1)
[x] California Environmental Protection Agency (CalEPA), & The Office of Environmental Health Hazard Assessment (OEHHA). (n.d.). 1,4-Dioxane. Retrieved February 18, 2019, from https://oehha.ca.gov/proposition-65/chemicals/14-dioxane
[xi] EWG and the Campaign for Safe Cosmetics. (2010, May). Not So Sexy. Retrieved February 18, 2019, from https://www.ewg.org/research/not-so-sexy
[xii] Draelos ZD. The science behind skincare: Cleansers. J Cosmet Dermatol. 2018; 17:8–14. doi:10.1111/jocd.12469
[xiii]Ertel, Keith. (2000). Modern skin cleansers. Dermatologic clinics. 18. 561-75. 10.1016/S0733-8635(05)70207-2
[xiv] Seweryn, A. (2018). Interactions between surfactants and the skin – Theory and practice. Advances in Colloid and Interface Science, 256, 242-255
[xv] Corazza, M., Lauriola, M. , Zappaterra, M., Bianchi, A. and Virgili, A. (2010), Surfactants, skin cleansing protagonists. Journal of the European Academy of Dermatology and Venereology, 24: 1-6. doi:10.1111/j.1468-3083.2009.03349.x
[xvi] Orsavova, J., Misurcova, L., Ambrozova, J. V., Vicha, R., & Mlcek, J. (2015). Fatty Acids Composition of Vegetable Oils and Its Contribution to Dietary Energy Intake and Dependence of Cardiovascular Mortality on Dietary Intake of Fatty Acids. International journal of molecular sciences, 16(6), 12871-90. doi:10.3390/ijms160612871
[xvii] Chularojanamontri, L., Tuchinda, P., Kulthanan, K., & Pongparit, K. (2014). Moisturizers for Acne: What are their Constituents?. The Journal of clinical and aesthetic dermatology, 7(5), 36-44.
[xviii] Lin, T. K., Zhong, L., & Santiago, J. L. (2017). Anti-Inflammatory and Skin Barrier Repair Effects of Topical Application of Some Plant Oils. International journal of molecular sciences, 19(1), 70. doi:10.3390/ijms19010070
[xix] Ventura, S. A. and Kasting, G. B. (2017), Dynamics of glycerine and water transport across human skin from binary mixtures. Int J Cosmet Sci, 39: 165-178. doi:10.1111/ics.12362
[xx] Burlando, B. and Cornara, L. (2013), Honey in dermatology and skin care: a review. J Cosmet Dermatol, 12: 306-313. doi:10.1111/jocd.12058
[xxi] Chularojanamontri, L., Tuchinda, P., Kulthanan, K., & Pongparit, K. (2014). Moisturizers for Acne: What are their Constituents?. The Journal of clinical and aesthetic dermatology, 7(5), 36-44
[xxii] Khnykin, D., Miner, J. H., & Jahnsen, F. (2011). Role of fatty acid transporters in epidermis: Implications for health and disease. Dermato-endocrinology, 3(2), 53-61
[xxiii] Porto, Carla & Decorti, Deborha & Tubaro, Franco. (2012). Fatty acid composition and oxidation stability of hemp (Cannabis sativa L.) seed oil extracted by supercritical carbon dioxide. Industrial Crops and Products. 36. 401–404. 10.1016/j.indcrop.2011.09.015