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.
The disrupted barrier becomes more reactive. The disrupted microbiome allows pathogenic organisms more access. The net result is more acne, not less.
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.
What people using baking soda for acne often report: initial seeming improvement, then worsening. This is predictable from the chemistry. The disrupted barrier becomes more reactive. The disrupted microbiome allows pathogenic organisms more access. The skin, trying to compensate for barrier damage, may increase sebum production. The net result is often more acne, not less — but with a delay between the disruption and the visible consequence that makes the connection 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.
The post-inflammatory hyperpigmentation from repeated baking soda use compounds. Each session raises the pH, disrupts the barrier, creates an inflammatory response, and adds to the cumulative melanocyte signal. People who have been using baking soda scrubs on their face for months while wondering why their skin tone is uneven are often looking at the result of this compounding.
This is not a hypothetical risk. It is the mechanism. The recommendation to use baking soda on skin — particularly for people managing PIH or hyperpigmentation — does direct and predictable harm.
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, a disrupted barrier means more inflammation, and more inflammation means a more visible, longer-lasting mark, so people using baking soda scrubs for months are often looking at the compounding result of exactly that cycle. 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.
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