What Do Soft Skin and the Way We Smell Have in Common?

What do soft, resilient skin and the way our skin smells have in common?

Part of the answer may lie in something we cannot see at all: the chemistry of our skin.

Healthy skin generally maintains a mildly acidic environment. You may have heard this discussed in connection with the acid mantle — perhaps on a cleanser promising to be “pH balanced,” or in skincare advice telling us that the ideal skin pH is 5.5.

But the biology is more interesting than the number on a bottle.

Skin pH influences processes involved in maintaining the skin barrier and helps shape the conditions in which billions of bacteria, fungi and other microorganisms live.

And those microorganisms are not simply passengers.

They interact with our skin, with one another and with substances our bodies release. In places such as the underarm, microorganisms can transform largely odorless components of our secretions into volatile molecules that we perceive as body odor.

Suddenly, skin pH becomes about much more than whether a cleanser says pH 5.5.

The question becomes particularly interesting after 40.

For many women, the forties mark the beginning of one of the most significant biological transitions of adult life: the menopausal transition.

Hormones do not simply decline in a straight line. As ovarian function changes, the hormonal patterns that have accompanied the reproductive years begin to shift. Estradiol can fluctuate considerably during the menopausal transition before eventually declining, while hormones such as FSH follow their own changing patterns.^[1]

And the skin does not exist outside this transition.

Sebum production may decline, skin can become drier and the lipids that help form its barrier can change. Because hormones interact with many aspects of skin biology, these shifts may also change the environment in which our skin and its microorganisms coexist.^[2][10]

And if skin pH does change, can we influence it ourselves?

Why Does Skin pH Matter for How Our Skin Looks, Feels and Smells?

To understand why pH matters, we need to look at what acidity actually does in the outermost layers of our skin.

The stratum corneum, the outermost layer of the epidermis, is a highly organized barrier. Its cells are surrounded by lipids that help keep water in, protect us from the outside world and maintain the conditions in which the skin can function.

And some of the processes that build and maintain this barrier are pH-sensitive.

Enzymes involved in producing important barrier lipids work best under acidic conditions. Other pH-dependent processes help control how connections between skin cells are broken down as old cells are shed from the surface. Together, these processes contribute to the organization, renewal and integrity of the stratum corneum.^[3][6]

And that biology can become something we actually see and feel.

When skin cells are shed in a controlled way and the lipids between them form an effective barrier, the stratum corneum is better able to retain water and maintain an organized surface. This helps skin feel soft and supple and appear smoother and more even. When these processes are disturbed, dryness, roughness and scaling can become more noticeable.^[3][6]

But pH does not matter only to our own skin cells.

The same chemical environment is also home to bacteria, fungi and other microorganisms. Different microorganisms vary in how well they tolerate acidic or more alkaline conditions. pH therefore becomes one of the conditions that helps shape the habitat in which the skin microbiome lives.^[3]

And what happens within that habitat does not necessarily remain invisible.

Microorganisms interact with substances found on our skin and can transform some of them into entirely different molecules. In the underarm, for example, bacteria convert largely odorless components of our secretions into volatile compounds that contribute to characteristic body odor.

So something as seemingly abstract as skin pH can connect to things we recognize immediately: how hydrated and smooth our skin feels, the environment in which its microorganisms live and even some of the chemistry behind the way we smell.

But where does this mildly acidic environment come from?

And what exactly are we describing when we call it the acid mantle?

What Is the Skin’s Acid Mantle and Why Does It Matter?

The term acid mantle sounds almost as if our skin were covered by a thin acidic coating.

But that picture is too simple.

Researchers today describe the acid mantle as buffering activity within the upper stratum corneum, the outermost part of our skin barrier, that helps create and maintain acidic conditions. It contributes to barrier integrity and is involved in microbial regulation, inflammation and structural stability.^[3]

Skin pH and the acid mantle are related, but they are not the same thing.

Skin pH is something we can measure. It tells us how acidic or alkaline the skin is at a particular place and moment.

The acid mantle refers to the biological processes that help create and maintain those acidic conditions.

So before asking whether we can change the acid mantle, we first need to understand the number most often associated with it.

What Is a Healthy Skin pH?

The pH scale describes how acidic or alkaline an aqueous environment is. A pH of 7 is neutral; values below 7 are acidic and values above 7 are alkaline.

Human skin generally maintains a mildly acidic surface.

You may have heard that healthy skin has a pH of 5.5.

It is a useful shorthand, but not a biological rule.

Skin pH varies between people and between different areas of the body. It can also change with washing, cosmetics and even the conditions under which it is measured.^[3][4][5]

Human studies suggest that natural skin-surface pH is often below 5.

In a multicenter study of 222 volunteers, the average pH measured on the inner forearm was 4.9 after participants had avoided water, topical products and intensive washing for 24 hours.^[5]

A separate study of 330 people found something remarkably similar. Average forearm pH fell from 5.12 to 4.93 after participants avoided showering and cosmetic products for 24 hours. From these and other observations, the researchers estimated the average “natural” skin-surface pH to be approximately 4.7.^[4]

Even something as ordinary as water can temporarily change what we measure. In the same study, exposure to tap water raised skin-surface pH for several hours before it moved back toward its previous acidic level.^[4]

This tells us something important:

So rather than asking:

a more useful question may be:

Is Skin pH 5.5 Really Ideal?

Probably not as a universal target.

The familiar number 5.5 should not be understood as a precise optimum that every person should try to achieve. Physiological skin pH varies, and measurements below 5 are common.^[3][4][5]

And there is another reason why reducing the acid mantle to a single surface measurement may be misleading.

Our understanding of how acidity is organized within the outer skin layer is evolving.

Recent experimental research suggests that acidity may not be distributed evenly throughout this layer. Instead, different depths may maintain different pH conditions.^[7]

This has so far been demonstrated in experimental models, and researchers are still investigating how closely the same organization applies to human skin.

So a pH value measured at the surface may capture only one part of a much more complex chemical environment.

Which brings us to another question:

If acidic conditions emerge from skin biology, could they change when the biology itself begins to change?

Does Skin pH Change After 40?

If the biology that helps maintain our skin’s acidity changes across adult life, we might expect skin pH to change with it.

And research suggests that it can.

But there is no simple trajectory in which skin becomes progressively less acidic as we get older.

What Does Research Show About Skin pH and Age?

In a study of 97 women between 20 and 97 years old, skin-surface pH increased slightly with age across the forehead, temple and forearm.^[8]

A larger study of 150 healthy women between 18 and 80 years old found something more intriguing.

Sebum production declined significantly with age, but skin pH did not simply continue rising. The highest average pH was measured in women between 50 and 60, while the oldest group had the lowest mean pH. The researchers also reported significantly higher skin-surface pH in menopausal women.^[9]

Independent experimental research adds another piece to the picture. In moderately aged human skin between 50 and 80 years, researchers found impaired acidification of the stratum corneum. Mechanistic experiments in an analogous mouse model linked higher pH to impaired lipid processing and increased activity of pH-sensitive serine proteases, while experimental acidification normalized several of these abnormalities.^[6]

So the available evidence does not describe one predictable “aging pH curve.”

And for women, that raises another question.

The period in which some studies observe differences in skin pH overlaps with the profound hormonal changes of the menopausal transition.

Could hormones be part of the explanation?

What Do We Know About Estrogen, Menopause and Skin pH?

At the moment, we cannot say that declining estrogen directly raises skin pH.

But hormones can influence parts of skin biology that may help determine the environment in which acidity is maintained.

One of those is sebum. Sebum production in women tends to decline across adult life, while studies in men show a comparatively more stable pattern.^[10]

Another is the lipid architecture of the skin barrier.

A small study comparing premenopausal women, postmenopausal women and postmenopausal women taking hormone replacement therapy found that postmenopausal skin contained lower levels of ceramides and ceramides of shorter average chain length. These differences were absent or reduced in the HRT group.^[11]

Ceramides are important lipids between the cells of the outer skin barrier. Their amount and composition help determine how effectively that barrier is organized and how well it limits water loss.

The researchers then found something particularly interesting.

Women with higher circulating estradiol tended to have greater ceramide abundance and longer ceramide chains. And when human skin cells were exposed to estradiol in the laboratory, production of certain ceramides increased.^[11]

This gives us evidence that estradiol can directly influence part of the skin’s ceramide metabolism.

But it does not show that estrogen directly controls skin pH.

The possible connection may be more indirect.

As hormones change, they may influence sebum, barrier lipids, hydration and other properties of the skin. These changes could, in turn, alter some of the conditions involved in maintaining its acidic environment.

So imagine measuring a higher skin pH in a woman in her early fifties.

The number alone cannot tell us why.

Is it chronological age? Her stage of the menopausal transition? Changes in sebum or barrier lipids? The area of skin being measured? The products she uses? How recently she washed?

Or several of these influences acting together?

Most of the studies we have are not designed to separate all of these factors.

So the evidence does not yet justify saying:

What it suggests is more interesting:

And those conditions do not belong to our skin cells alone.

They are also the habitat of the skin microbiome.

How Does Skin pH Affect the Skin Microbiome?

Our skin is home to bacteria, fungi and other microorganisms.

Like all living organisms, they thrive under particular conditions.

Some prefer warmer environments, others cooler ones. Some grow better where there is more moisture. And on our skin, the availability of substances such as sebum can help determine which microorganisms find the conditions they need.

Acidity is another part of that environment.

Different microorganisms vary in how well they tolerate acidic or more alkaline conditions. Skin pH can therefore help shape which microorganisms are able to thrive in a particular area of our skin.^[3]

In this sense, our skin is not simply a surface on which microorganisms happen to live. Its temperature, moisture, sebum and pH together help create their habitat.

But microorganisms do not only respond to the habitat our skin provides.

They can change it too.

As microorganisms use substances found in sweat, sebum and other skin secretions, they produce metabolites of their own. Those metabolic activities can alter aspects of their immediate environment.^[3]

This is also why the skin microbiome cannot easily be divided into “good” and “bad” microorganisms.

The same organism may behave differently depending on where it lives, what nutrients are available, which other microorganisms are present and the condition of the surrounding skin.

And if pH helps shape those conditions, it raises an obvious possibility: perhaps changing pH could also change the microbial community.

Can Changing Skin pH Change the Skin Microbiome?

In principle, yes. Changing pH changes one of the environmental conditions microorganisms encounter.

But living human skin is more complicated.

A small 2025 study in postmenopausal women found that although some low-pH skincare formulations lowered skin-surface pH, this did not consistently change the overall microbial community.^[12]

Skin is continually changing the habitat too. It produces sweat and sebum, renews its outer layers and encounters water, skincare products and the environment around us.

Its microorganisms are living within those changing conditions, interacting with our skin and with one another.

And some of the molecules produced through their metabolism have an effect we can actually perceive.

We can smell them.

Can Skin pH Affect Body Odor?

Sweat has a reputation it does not entirely deserve.

When we notice body odor after sweating, it is easy to assume that sweat itself is what smells.

But particularly in the underarm, much of the characteristic odor develops only after microorganisms become involved.

Our underarms contain several types of glands that release water, salts, lipids, proteins and other substances onto the skin. Many of these secretions are initially odorless or have very little odor.^[13]

The smell develops when microorganisms begin to metabolize some of them.

Microbial enzymes transform components of these secretions into smaller, volatile molecules that can travel through the air and reach our nose. Research has identified several microbial pathways involved in this process, with Corynebacterium playing an important role in producing characteristic axillary odorants.^[13]

And this brings us back to pH.

If acidity helps shape the conditions in which microorganisms live, could changing those conditions also influence the chemistry that produces odor?

How Are Skin pH, Bacteria and Body Odor Connected?

There is evidence that acidity matters to some of the microorganisms involved in underarm odor.

Corynebacteria isolated from human underarms showed markedly lower survival at pH 5 than at pH 6.^[14] Earlier experimental research also found that odor production by cultured corynebacteria was greatest around pH 6.^[15]

That difference is important because human underarm skin naturally tends to have a somewhat higher pH than many other areas of the body.

This suggests that lowering underarm pH could make the environment less favorable for some odor-producing Corynebacteria and potentially reduce their contribution to body odor.

So have we found the solution to body odor?

Not quite.

pH is only one part of the chemistry behind body odor.

The odor that ultimately develops depends on what our skin releases, which microorganisms are present and how they metabolize those secretions. Moisture, washing and the products we use can further influence the conditions in which this chemistry unfolds.

So rather than thinking of body odor as simply a question of sweat or bacteria, a more accurate picture begins to emerge:

This also helps explain why changing pH is an interesting strategy in deodorant formulation. It does not necessarily require eliminating the microorganisms living on our skin. Changing their environment may itself influence how well certain odor-producing microorganisms thrive and how actively they produce odor-related compounds.

And that leads to the next question:

If skin pH can influence this environment, how much can we actually change it?

Can We Change Our Skin pH?

Yes, at least to some extent.

We have already seen that water, cleansing and skincare can temporarily shift the pH measured at the skin surface. But our skin does not simply remain at whatever pH it encounters. Its own buffering processes continually work to maintain its acidic environment.

So the more interesting question is:

Can repeated skincare change skin pH for longer, and does that make a meaningful difference to the skin itself?

Independent experimental research helps explain why acidification may matter. In moderately aged skin, impaired stratum corneum acidification has been linked to changes in pH-sensitive lipid processing and the premature breakdown of connections between skin cells. Experimental acidification normalized several of these abnormalities in the experimental model.^[6]

And controlled research in older adults suggests that external acidification can also influence measurable properties of human skin.

In one controlled study, researchers compared the same water-in-oil formulation adjusted to pH 4.0 or pH 5.8.^[16]

After four weeks, the pH 4 formulation had lowered skin-surface pH and was associated with better barrier integrity and less roughness and scaling. In a separate barrier-disruption experiment within the same study, it also accelerated early barrier recovery.^[16]

A follow-up study looked more closely at what was happening within the skin barrier.

Between the cells of our outer skin layer lie highly organized layers of lipids, known as intercellular lipid lamellae. They help keep water from escaping and are an important part of an intact skin barrier.

What the researchers found was encouraging: even in older skin, some features of the barrier appeared responsive to changes in its external environment.

After four weeks, the pH 4 formulation was associated with greater hydration and more pronounced improvements in the organization of these lipid layers than the pH 5.8 formulation.^[17]

So changing skin pH did not simply change a number measured on the surface. In these studies, it was accompanied by measurable differences in how older skin looked, felt and functioned.

Is a Lower Skin pH Better?

This is where we need to be careful.

The studies do not tell us that everyone should use skincare at pH 4. They investigated particular formulations in older adults under controlled conditions.

And pH is only one characteristic of a skincare product.

The ingredients surrounding it, how the product is formulated, how often it is used and the condition of the skin all influence what happens after we apply it.

An acidic product can still irritate. Two products with exactly the same pH can behave very differently on our skin.

And that changes the practical question.

Instead of asking “What pH should my skincare have?”, perhaps we should ask:

How Can We Support Healthy Skin pH After 40?

If skin pH can be influenced from the outside, what does that mean for everyday skincare?

Probably not that we should start measuring our skin or trying to keep it at precisely 4.7, 5.0 or 5.5.

Our skin already has biological processes that continually work to maintain its mildly acidic environment.

So rather than trying to control a number, the more useful approach may be to protect the conditions that allow skin to regulate itself.

How Does the Skin Barrier Help Maintain pH?

The relationship between skin pH and the barrier works in both directions.

As we have seen, acidic conditions support pH-sensitive processes involved in barrier lipids and the normal shedding of skin cells. But the barrier itself also contributes to the environment in which skin acidity is maintained.

This becomes particularly relevant after 40.

As hormonal patterns change across the menopausal transition, sebum production, hydration and barrier lipids can change too. Skin may become drier and less resilient to repeated disruption.

That does not mean we should avoid cleansing.

But how we cleanse matters.

Traditional soaps can be strongly alkaline and temporarily raise skin-surface pH. Modern cleansers, however, can be formulated within a mildly acidic range that is closer to the skin’s natural environment.^[3]

But pH alone does not tell us whether a cleanser is gentle.

The cleansing agents it contains, how strongly it removes skin lipids, how often it is used and the condition of the skin itself all influence what happens after cleansing.

The same caution applies to acids.

Ingredients such as lactic acid, glycolic acid and salicylic acid can make a formulation more acidic. But they also interact with the skin in their own ways, for example by influencing how cells are shed from its surface.^[18] Their effects therefore cannot be explained by pH alone.

So what do we actually mean when we talk about supporting the acid mantle?

Perhaps the easiest way to think about it is to imagine our skin as a tiny living world.

Skin cells, lipids, sweat, sebum and microorganisms all share this environment. And just like any living habitat, the conditions within it help determine what can thrive there and how well the whole community functions.

Supporting the acid mantle means helping our skin maintain the mildly acidic conditions in which this world has evolved to live.

That does not mean trying to eliminate its microbial inhabitants. Quite the opposite. It means avoiding changes that repeatedly disturb their habitat or create conditions that may favor organisms we would rather not encourage.

Strongly alkaline products, repeated stripping of barrier lipids or unnecessary irritation can all interfere with parts of this environment. Gentle cleansing, preserving barrier lipids and supporting hydration can help give the skin something more valuable: the conditions in which it can regulate itself.

In that sense, supporting the acid mantle is less about adding something the skin is missing and more about taking care of the little world that is already there.

But what if we are doing everything right — and our skin still begins to change?

We may cleanse gently, protect barrier lipids, support hydration and avoid unnecessarily alkaline or irritating products. And yet the environment of our skin may still shift.

Because supporting the acid mantle is about more than choosing the right skincare.

Not every influence reaches our skin from the outside. Some begin within the body itself.

Hormonal changes are one example. Across the menopausal transition, changing hormonal patterns can influence sebum production, hydration and the lipids that help build our skin barrier.

Estradiol itself appears to influence the production and composition of ceramides, important lipids that help our skin retain water and maintain its barrier.^[11] As these parts of skin biology change, the conditions from which its acidic environment emerges may change with them.

Medications may add another layer. Systemic antibiotics, in particular, can alter microbial communities on the skin.^[19] How these changes translate into lasting effects on skin pH or the acid mantle is far less clear.

And there may be other influences from within.

Observational research has found associations between skin-surface pH and nutritional status, dietary intake and metabolic health.^[20][21][22]

None of this means that hormones, medications or what we eat determine our skin pH in a simple or predictable way. Much of this research is still emerging.

But it raises a fascinating possibility:

Supporting the acid mantle may therefore mean more than choosing the right cleanser or looking for the right pH on a bottle. It means understanding the many influences that help our skin maintain the living environment in which its cells and microorganisms coexist.

Does pH-Balanced Skincare Really Matter?

So what should we make of a cleanser or moisturizer labelled pH balanced?

It can be useful information, but it tells us only one thing about the formulation.

A cleanser at pH 5.5 may be closer to the naturally acidic conditions of skin than a traditional alkaline soap. But the number alone cannot tell us how gently it cleanses, how much it disturbs barrier lipids or how a particular person’s skin will respond.

pH matters. But formulation matters too.

For skin after 40, that means looking beyond the number on the bottle: gentle cleansing, preserving barrier lipids, supporting hydration and avoiding unnecessary irritation all help protect the environment in which skin regulates its own chemistry.

What Are We Still Learning About Skin pH After 40?

We now know that skin pH is about much more than a number.

The mildly acidic environment of our skin helps support processes that influence how soft, smooth and resilient our skin feels and appears. It also helps shape the habitat of the microorganisms living on our skin — including some of those involved in the chemistry of body odor.

And we know that this environment is not fixed. Skin pH can shift with water, cleansing and skincare, and studies suggest that it can also differ across age and stages of adult life.

But one much bigger question remains:

Studies have observed differences in skin pH across age and around the menopausal transition. But they have not established why those differences occur.

Is changing hormonal biology involved?

Possibly.

Hormones can influence sebum, hydration and barrier lipids, all of which are part of the environment in which skin acidity is maintained. But we do not yet know whether hormonal changes themselves alter skin pH, how large such an effect might be or whether the relationship is indirect.

The same uncertainty becomes particularly interesting when we think about body odor.

And what if the way we smell begins to change during midlife? What exactly could be changing?

Is it the composition of sweat or sebum? The microorganisms metabolizing those secretions? Skin pH? Hormonal changes? Metabolic health? Medications?

Or several of these influences interacting with one another?

We do not yet know.

Nor do we know whether deliberately changing skin pH can predictably reshape the microbiome over time, or how much naturally occurring differences in pH contribute to differences in body odor outside experimental conditions.

These questions reveal a larger gap in our understanding.

Research has examined many of these pieces separately: skin pH, barrier function, the microbiome, hormonal changes and body odor.

What we have far less of is research showing how they interact within the same changing biological environment.

Following women through the menopausal transition while measuring hormones, skin pH, sebum, barrier properties and microbial communities — and perhaps even odor-related metabolites — could begin to show whether these changes actually move together, which appear first and which may be connected.

Until then, we should be careful not to turn an intriguing biological connection into an established causal pathway.