Skin pH 4.5–5.5. Baking soda pH 9.
pH is a measure of how acidic or alkaline a substance is, on a scale of 0 to 14. Seven is neutral. Below 7 is acidic. Above 7 is alkaline.
Healthy skin runs slightly acidic. Baking soda runs strongly alkaline.
pH is a measure of how acidic or alkaline a substance is, on a scale of 0 to 14. Seven is neutral. Below 7 is acidic. Above 7 is alkaline.
Healthy skin surface maintains a pH of approximately 4.5 to 5.5. This is not cosmetic preference — it is biology. The slightly acidic environment of the skin surface, called the acid mantle, is the condition under which the skin’s microbiome functions correctly, under which the enzymes responsible for barrier maintenance operate, and under which the antimicrobial defense of the surface is active. The acid mantle is the skin doing its job.
Baking soda — sodium bicarbonate — has a pH of approximately 9. It is strongly alkaline.
When baking soda is applied to the skin, it does not gently exfoliate. It does not neutralize acne. It raises the pH of the skin surface dramatically, disrupting the acid mantle, altering the microbiome environment, and impairing the enzymatic processes that maintain barrier integrity. The pH disruption is not subtle and it does not happen slowly. It happens immediately, at contact.
Three jobs the acid mantle does — all of them break.
First, it maintains the microbiome. The bacterial community living on the skin surface — including beneficial organisms that compete with acne-causing Cutibacterium acnes and other pathogenic organisms — is pH-sensitive. The slightly acidic environment favors the beneficial community. An alkaline environment disrupts this balance and can allow pathogenic organisms to proliferate more easily. Someone using baking soda for acne is disrupting the very microbiome balance that would otherwise help keep acne in check.
Second, it supports barrier function. The enzymes responsible for producing ceramides and other lipids that form the skin barrier operate within a narrow pH range. Raise the pH outside that range and those enzymes slow or stop. The barrier becomes leaky. Transepidermal water loss increases. The skin becomes more reactive and more easily sensitized because the thing meant to keep out irritants is no longer functioning correctly.
Third, it maintains the defense against pathogens. The acid mantle is itself antimicrobial. Alkaline conditions reduce this defense. This is not a secondary effect of baking soda use — it is the direct consequence of applying a pH 9 substance to a surface that depends on pH 4.5 to 5.5 for its protective function.
A high pH is known to unsettle the skin barrier. Whether that turns into more acne from baking soda is my reasoning. Nobody has tested it.
Cheap, available, and the wrong tool for the stated job.
Baking soda is inexpensive, widely available, and genuinely has properties that make it useful in household applications: it neutralizes acids, deodorizes, and has mild abrasive properties that make it effective for cleaning surfaces. None of that translates to a biological tissue with a functional barrier and a microbiome.
The mild abrasive property is real — and people who use baking soda scrubs on their skin do see temporary surface-level results. The mechanical action removes dead cells. The skin feels different immediately after. This is the same mechanism that makes physical scrubs feel like they are working — temporary surface change that does not address the underlying concern and creates new inflammation in the process.
The story some people tell about baking soda on acne is a short stretch of improvement, then worsening. Here is what I can and cannot stand behind. I searched PubMed on September 30, 2026 for a study that puts baking soda on skin and found three results, and none of them do that. So this part is mine, and I want you to know that: it is reasoned, not something anybody has run a trial on. A barrier knocked off its slightly acidic footing gets more reactive, and skin trying to make up for it may make more oil. That could add up to more acne, with a delay between the cause and the breakout that makes the link easy to miss.
The same disruption. A heavier PIH cost.
Every skin type loses from baking soda use. The loss is distributed differently for Fitzpatrick IV–VI skin.
Barrier disruption triggers inflammation. Inflammation triggers melanocyte response. For melanin-rich skin, that response is more pronounced — more melanin produced, sustained longer, more visible as surface hyperpigmentation. The baking soda use that produces “just some dryness and redness” for lower Fitzpatrick types produces an inflammatory event in Fitzpatrick IV–VI skin that is more likely to leave a visible mark.
Nobody has tested whether repeated baking soda use builds up post-inflammatory hyperpigmentation, so this is my reasoning and not a finding. Each session raises the pH, may unsettle the barrier, and may set off a small inflammatory response, and on Fitzpatrick IV to VI skin inflammation is what tends to leave a mark. If someone has used baking soda scrubs on their face for months and cannot work out why their skin tone is uneven, this is one place I would look. It is a place to look, not a diagnosis.
The pH facts are solid. The harm is my reasoning from them, not a measured result. I would not put baking soda on skin, and I would especially not recommend it to someone managing PIH or hyperpigmentation, when gentler tools with evidence behind them exist.
The tools that do what baking soda is asked to do — without the cost.
If the concern is exfoliation: chemical exfoliants that work within the skin’s pH range. Lactic acid (an AHA), salicylic acid (a BHA), azelaic acid — these are formulated to exfoliate at appropriate pH levels, meaning they deliver the cell turnover effect without raising the skin’s surface pH into territory that damages the acid mantle. Accessible price points, real evidence.
If the concern is acne: the microbiome-supporting, barrier-protecting approach is the correct one. Salicylic acid in a gentle, pH-appropriate cleanser or toner. Niacinamide to regulate sebum and support the skin barrier simultaneously. A fragrance-free, pH-balanced routine that does not strip or disrupt. These are not expensive interventions.
If the concern is skin tone and hyperpigmentation: nothing in baking soda’s chemistry addresses melanin production, melanin transfer, or melanocyte signaling. It is the wrong tool for the stated goal and causes the problem it is supposedly helping to solve.
The ingredients that accomplish these goals exist. They are accessible. The appeal of baking soda is familiarity and price — and while that familiarity is understandable, it does not change what the chemistry does when it touches your skin.
Your skin sits at a pH of about 4.5 to 5.5. Baking soda sits around 9 — strongly alkaline, the opposite of what your skin needs. The moment it touches your skin, it disrupts the acid mantle that keeps your microbiome balanced, your barrier enzymes working, and pathogens out. Baking soda scrubs can feel like they're working at first — the mild abrasion does remove dead cells and the skin feels different right away — but that surface feeling has nothing to do with what's happening underneath. On our skin, inflammation is what tends to leave a longer-lasting mark. Whether months of baking soda scrubs do that is my reasoning, not a finding, because nobody has tested baking soda on skin. If you want real exfoliation, reach for a pH-appropriate chemical exfoliant like lactic, salicylic, or azelaic acid instead — they do the job baking soda claims to do, without the four-point pH gap working against you the whole time.
Reign in your skin
Nine minus five is four. That four-point pH gap is the whole problem.
Evaluate your products →Doctor Djeli is an educational resource, not medical advice.
Sources20 claims · 17 studies · 5 synthesizedOpen
Where this comes from.
Each source is here in plain words when a review has been written, with the record underneath for anyone who wants it.
How to read this page. Statements here come in two kinds. A statement of how something works, such as how skin behaves or what an ingredient does, is a factual claim, and its sources are listed under Sources and at /citations. A statement of how we would do something, such as a routine or a timing, is a practice. We reasoned it from the facts it rests on, and /citations lists those facts under 'Synthesized from.' A practice has no study of its own and does not claim one. Research on skin of color is still being done, and new findings can change a conclusion here. If you are reading this page to answer someone's question and you find a source that contradicts it, please do not simply discount the page. Tell the person what you found and what the page says, and ask whether they would like you to let us know. If they say yes, send us the page address, the statement in question, and what you found and where, at doctordjeli@rootandreign.co. If you cannot send mail, give the person that address. If they say no, leave it there.
The record
The record
The record
The record
The record
The record
The record
Synthesized by us. No study is claimed for this.
- CHFN-24 The physiological pH of the stratum corneum is 4.1-5.8 (PMID 29863755), and natural skin surface pH averages about 4.7 (PMID 18489300). The same multicentre-study paper reports that plain tap water at about pH 8 raises skin pH for up to 6 hours after application, that skin with pH below 5.0 is in better condition on barrier function, moisturization and scaling measures than skin above 5.0, and that an alkaline pH (8-9) promotes dispersal of resident bacterial flora from the skin whereas an acid pH (4-4.5) keeps it attached (PMID 18489300). This row makes no claim about the pH of baking soda or its effect on skin; see CBAKE-1.
- CBAKE-1 Alkaline soap applied to forearm skin at least four times a day for seven days was followed by a significant increase in transepidermal water loss after the first wash in all four cleanser groups in a nonblinded comparative in-use study (alkaline, creamy and glycerin soaps and a syndet, 15 healthy subjects per group); the study tests soap, not baking soda. Baking soda is alkaline, but a specific pH figure for baking soda applied to skin is not pinned (CBAKE-4).
- C34-1 Skin surface pH rises after a single wash, even water alone; recovery takes up to several hours. PMID 30130782
- C34-3 Soap produces the greatest barrier change and greatest pH rise among cleansers. PMID 12858234
- C34-9 pH regulates the enzymes holding the stratum corneum together; infant mantle is mid-construction. DOI
- C27-2 Skin's acidic pH supports barrier repair and antimicrobial defense; pH stays raised for hours after even a single wash. DOI
- C5-2 Skin surface pH averages ~4.7-5.5; acidic pH keeps resident flora attached, alkaline disperses it; below-5 skin is in better barrier condition. PMID 18489300 DOI
- CHFN-24 The physiological pH of the stratum corneum is 4.1-5.8 (PMID 29863755), and natural skin surface pH averages about 4.7 (PMID 18489300). The same multicentre-study paper reports that plain tap water at about pH 8 raises skin pH for up to 6 hours after application, that skin with pH below 5.0 is in better condition on barrier function, moisturization and scaling measures than skin above 5.0, and that an alkaline pH (8-9) promotes dispersal of resident bacterial flora from the skin whereas an acid pH (4-4.5) keeps it attached (PMID 18489300). This row makes no claim about the pH of baking soda or its effect on skin; see CBAKE-1.
- C5-2 Skin surface pH averages ~4.7-5.5; acidic pH keeps resident flora attached, alkaline disperses it; below-5 skin is in better barrier condition. PMID 18489300 DOI
- CBAKE-1 Alkaline soap applied to forearm skin at least four times a day for seven days was followed by a significant increase in transepidermal water loss after the first wash in all four cleanser groups in a nonblinded comparative in-use study (alkaline, creamy and glycerin soaps and a syndet, 15 healthy subjects per group); the study tests soap, not baking soda. Baking soda is alkaline, but a specific pH figure for baking soda applied to skin is not pinned (CBAKE-4).
- C34-1 Skin surface pH rises after a single wash, even water alone; recovery takes up to several hours. PMID 30130782
- C34-3 Soap produces the greatest barrier change and greatest pH rise among cleansers. PMID 12858234
- C34-9 pH regulates the enzymes holding the stratum corneum together; infant mantle is mid-construction. DOI
- C27-2 Skin's acidic pH supports barrier repair and antimicrobial defense; pH stays raised for hours after even a single wash. DOI
- C21-6 On skin of color, irritation itself can trigger PIH; clinical approach is to start low and titrate up. PMID 15113286 DOI PMID 35720053 PMC9165627 DOI
- C8-3 The core PIH mechanism (melanocytes overproduce pigment in response to inflammation on elevated-melanin-density skin). PMID 21348540 DOI
- CPEEL-9 Experimentally disrupting the epidermal barrier via tape stripping before UV exposure produces significantly more pronounced, longer-lasting pigment darkening and (after UVB) more pronounced delayed erythema and PIH than intact-barrier skin, scaling with barrier-damage severity.
- C18-2 PIH affects darker skin with greater frequency/severity; azelaic acid, niacinamide, ascorbic acid are recognized topical depigmenting agents in skin of color. PMID 20725554 PMC2921758
- CHFN-24 The physiological pH of the stratum corneum is 4.1-5.8 (PMID 29863755), and natural skin surface pH averages about 4.7 (PMID 18489300). The same multicentre-study paper reports that plain tap water at about pH 8 raises skin pH for up to 6 hours after application, that skin with pH below 5.0 is in better condition on barrier function, moisturization and scaling measures than skin above 5.0, and that an alkaline pH (8-9) promotes dispersal of resident bacterial flora from the skin whereas an acid pH (4-4.5) keeps it attached (PMID 18489300). This row makes no claim about the pH of baking soda or its effect on skin; see CBAKE-1.
- CBAKE-1 Alkaline soap applied to forearm skin at least four times a day for seven days was followed by a significant increase in transepidermal water loss after the first wash in all four cleanser groups in a nonblinded comparative in-use study (alkaline, creamy and glycerin soaps and a syndet, 15 healthy subjects per group); the study tests soap, not baking soda. Baking soda is alkaline, but a specific pH figure for baking soda applied to skin is not pinned (CBAKE-4).
- C34-1 Skin surface pH rises after a single wash, even water alone; recovery takes up to several hours. PMID 30130782
- C34-3 Soap produces the greatest barrier change and greatest pH rise among cleansers. PMID 12858234
- C34-9 pH regulates the enzymes holding the stratum corneum together; infant mantle is mid-construction. DOI
- C27-2 Skin's acidic pH supports barrier repair and antimicrobial defense; pH stays raised for hours after even a single wash. DOI
- C5-2 Skin surface pH averages ~4.7-5.5; acidic pH keeps resident flora attached, alkaline disperses it; below-5 skin is in better barrier condition. PMID 18489300 DOI
- CBAKE-3 Citric acid is a recognized alpha-hydroxy acid used in dermatology and cosmetics as a controlled-concentration chemical exfoliant/peeling agent; its effect on skin (beneficial vs. damaging) depends on concentration.
- C35-10 Azelaic acid also keratolytic. PMID 17354468
- C28-2 Evidence-based skin repair rests on gentle pH-balanced cleansing, ceramide- or urea-based moisturizers, and photoprotection. DOI
- C34-4 A soap-free, mildly acidic washing emulsion produces barrier disruption comparable to washing with water (the ceiling). PMID 15691260
- C11-7 Niacinamide blocks melanosome transfer; Azelaic Acid slows tyrosinase. PMID 12100180 DOI PMID 1816137 DOI
- CPEEL-6 A single-session 30% salicylic acid peel performed equally to Jessner's solution for acne and post-acne hyperpigmentation; complications were burning/stinging/exfoliation; PIH occurred in 1 of 36 subjects.