Skin acidity (pH): Small Number, Big Impact to our skin and microbiome?
- Marcelline Goyen
- Jul 3, 2025
- 7 min read
Updated: Dec 11, 2025
Table of content:
Introduction
You might already know a thing or two about skin acidity (pH) and its impact on skin health and skin microbiome. Yet, many skin professionals still have little or no knowledge of this topic. During my research on the skin-gut connection, I discovered that knowledge of skin pH is essential for making the right choices for effective skin care, skincare products, and skincare advice. All these choices also influence our skin microbiome. That's why, after extensive research, I wrote an entire chapter on this topic in both of my books.
Question about the skin acidity (pH)
Recently I asked a question on social media (Instagram and LinkedIn) and I was surprised about the answers I received, even from skin professionals, doctors and therapists.
My Question: "What’s the average pH of the skin?" I posted this question as a quiz last week — and wow, the responses came flooding in!
The answer: The correct answer is pH 4,7. But unfortunatelly most people chose 4.1, 5.0, or 5.5!!
But let’s be honest… many (para)medical professionals and skin therapists got it wrong. Surprising? Maybe. Then again… maybe not. The skin’s pH is still an overlooked topic, even though it plays a starring role in skin health, immune defense, and barrier function. That’s a bit worrying — because pH is crucial.Time for more healthcare professionals to dive into this topic! In my books, I explain in detail why skin pH matters and, more importantly, how to apply that knowledge in practice. You’ll find a brief summary on skin pH below.
The acidity of the skin, also known as the skin pH
One of the key factors for maintaining healthy skin is its specific pH level. The skin surface has an acidic pH and is therefore often referred to as the “acid mantle.” This acidity and the buffering capacity of the outermost layer of the skin, the stratum corneum (SC), are essential for healthy skin. They help maintain a balanced skin microbiome and support key physiological processes such as the formation of an optimal lipid barrier structure and the overall equilibrium in the SC.
As early as 1892, the acidic nature of the skin was first described. In 1982, Heuss concluded that "the entire healthy skin shows an acidic reaction, although the pH varies depending on the area of the body." It wasn’t until the 1920s and 30s that researchers began to recognize the role of surface pH in microbial defense. It was noted that sweat residues evaporate and leave behind a more concentrated, acidic layer. However, the acid mantle is not the only defense mechanism — sebum and the continuous shedding of skin cells also play a role in this protective function.
For a long time, it was believed that the skin’s acidity was primarily a result of exocrine secretions from glands, helping to regulate the skin’s flora and assist in cleansing. However, more recent studies have provided greater insight into the development, components, and role of skin pH, even in the deeper layers of the stratum corneum. The acidic environment plays a central role in maintaining the barrier function, normal lipid maturation, and healthy desquamation (shedding) of the skin.
In the early 20th century, researchers Schade and Marchionini (1928) discovered that covered skin is less acidic than skin exposed to the atmosphere, and that pH varies by body region. They assumed this was due to the impregnation of the stratum corneum with acidic sweat components, since areas with apocrine glands or skin folds showed a more neutral or even alkaline pH. Since the 1950s, the development of the flat glass electrode has allowed for more accurate pH measurements on the skin surface.
Why is the skin acidity so important?
The acidity of the skin plays a crucial role in:
Maintaining the barrier function of the stratum corneum;
Preserving the integrity and cohesion of the SC;
Supporting overall skin homeostasis;
Aiding in lipid production and barrier formation;
Supporting extracellular lipid processing;
Regulating proteolytic enzyme activity, crucial for proper desquamation;
Sustaining a healthy resident skin flora;
Ensuring antimicrobial resistance through a stable acidic environment.
Even slight deviations in pH can disrupt these processes. Recent scientific studies have shown that the skin pH differs in conditions such as acne, eczema, rosacea, and aging skin. But the big question remains: Is an altered pH the cause of these issues, or a consequence of other underlying factors?
External factors & product choice matter
In recent years, there has been growing scientific interest in how external influences — such as water, sweat, skincare products, and cleansers — affect the skin’s pH. Surprisingly, this knowledge is rarely applied in practice. Only a few skincare brands produce products with a pH that matches healthy skin — and clearly indicate this on the label. For most other cosmetic and skincare products, the pH is either unknown or kept secret under the label of "proprietary formula."
To better understand the development and treatment of skin disorders, insight into skin pH and the impact of external influences is essential — not only for dermatologists and skin therapists prescribing or recommending products, but also for manufacturers and individual users. This knowledge can improve everyday skin care, both for healthy skin and for preventing or managing sensitive or damaged skin.
Skin acidity pH advice for our skin microbiome
When choosing skincare products, don’t just look at the ingredients — also check the pH. Prevention is always better than cure! And read my book for more details about skin acidity and the impact on our skin microbiome.
Books about skin acidity (pH)
Go to my website page Our books, for information & ordering Englisch, Dutch and German skin-gut-axis books!
With love,
Marcelline Goyen, BSc skin therapy (dermal therapist) & author
FAQ – Skin Acidity (pH), the Acid Mantle & Skin Microbiome
1. Q: What is the normal pH of healthy skin?
A: The average pH of healthy skin is around 4.7, which means the skin’s surface is naturally acidic. This acidity — also called the acid mantle — is essential for maintaining the skin’s microbiome, barrier function, and immune defense. Even slight deviations from this value can influence skin health, inflammation, and susceptibility to skin conditions.
2. Q: Why is the skin’s acidity (acid mantle) so important?
A: Skin acidity plays a central role in: maintaining the barrier function of the stratum corneum, supporting lipid production and proper barrier formation, enabling healthy enzymatic activity for normal desquamation, preserving microbiome balance and protecting against pathogenic microorganisms. When the pH becomes less acidic (more neutral or alkaline), these processes are disrupted. Research shows altered skin pH in acne, eczema, rosacea, and aging skin — though it remains unclear whether pH imbalance is the cause or the result of these conditions.
3. Q: What factors influence the skin’s pH?
A: Skin pH is shaped by a combination of internal and external factors, including: water exposure (shower, swimming), sweat, cleansers and skincare products, occlusion (covered vs. uncovered skin), structural and lipid changes in the stratum corneum.
Many skincare products are not formulated at the skin’s natural acidity, and their pH is often not shown on the label. Understanding how these factors influence skin pH is essential for supporting the skin barrier and microbiome.
4. Q: How do I choose skincare products that support a healthy skin pH and microbiome?
A: Look beyond ingredients and check — or ask for — the product’s pH value. Ideally, products should align with the skin’s natural acidity (around pH 4.7). This supports barrier function, healthy microbial balance, and reduces irritation. Only a few brands consistently formulate products at skin-friendly pH levels, so conscious selection is important.
For a deeper understanding of how pH influences the microbiome, skin disorders, and effective skincare strategies, you can find more in my book The Amazing World of the Skin-Gut Axis.
5. Q: What if I don’t know the pH of a skincare product? Is that a problem?
A: Not necessarily — but it can be.Many cosmetic brands do not list the pH of their products, making it difficult to determine whether they support or disrupt the skin’s natural acidity. A product with a pH that is too high (more alkaline) can weaken the acid mantle, alter the skin microbiome, and impair barrier function. If the pH is not indicated: check whether the brand provides pH information on its website. Look for terms like “pH-balanced” or “acid mantle-friendly”, though these are not always scientifically regulated. And pay attention to how your skin responds — tightness, dryness, burning or prolonged redness may indicate that the product’s pH is not optimal. When in doubt, choose formulations specifically developed with the skin’s natural pH in mind, or consult a skin professional for guidance.
6. Q: When should I suspect that my skin pH is disturbed?
A: A disrupted skin pH often shows up as early changes in barrier function or microbiome balance. You might suspect pH imbalance if you notice: increased dryness, tight sensation, or flakiness, redness, burning, or stinging after cleansing, worsening of skin conditions such as acne, eczema, rosacea, or sensitive skin, slower healing of small wounds or irritations, more frequent breakouts or inflammation or a general sense that skincare products “don’t work anymore”. These signs suggest that the acid mantle may be compromised, affecting lipid processing, enzymatic activity, and microbial balance. Restoring the skin’s natural acidity — through skin-friendly pH products and simplified skin routines — can significantly improve barrier health and overall skin function.
Ps 1: In future blog posts, I will explore this topic further. I’d love to hear your thoughts, experiences, or questions in the comments. Your feedback is always welcome!
Ps 2: Feel free to share this blog with your network so more people dealing with skin problems can benefit from this knowledge. Just click one of the buttons below. Thanks so much!
Ps 3: If you would like to receive an author's copy to write a review about, I can arrange that for you. And if you have any questions, I'd love to hear from you. In my Bookshop 'our books' on my website www.skin-gut-axis.com you can find this book, including the Table of Content, and also the other books I wrote about the skin-gut axis.
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