Skin pH: why poorly formulated cleansers weaken the skin

Reading time: 6-8 min

Important note: this article provides general cosmetic and scientific information. It is not a substitute for medical advice and does not constitute a diagnosis.

Introduction

The term "gentle cleanser" is often used to describe a sensation. However, the gentleness of a cleanser is also a question of chemistry.

pH is one of them. Because it influences the organization of the stratum corneum, the activity of certain skin enzymes, the cohesion of lipids... and, ultimately, your daily comfort.

The key point: repeated cleansing, day after day, can either support skin stability or slowly erode it. The difference often comes down to formulation details.

Skin pH: natural, useful and measurable acidity

The skin's surface is physiologically slightly acidic. This acidity contributes to the balance of the cutaneous microbiota and to better barrier quality (hydration, desquamation, cohesion of the horny layer).

In a highly cited review, Lambers et al. show that cutaneous pH values below 5 are associated with skin in "better condition" than higher values, via biophysical measures such as hydration and barrier.

Why too high a pH after cleansing can be a problem

When a cleansing product (or even tap water, which is often alkaline depending on the region) raises the surface pH, the skin generally returns to its basal pH after a few hours. But the point isn't "once". It's the repetition.

The more the pH is repeatedly raised, the more likely you are to see a classic trio appear:

• dryness (tightness, roughness),
• discomfort (tingling sensations),
• more fragile barrier (more reactive, less tolerant skin).

Older (but robust) studies have also observed that higher pH values can be associated with a less effective barrier (higher TEWL) and lower hydration.

What science says about "soap" vs "syndet

The word "soap" is sometimes used to designate all cleansers. However, when formulated, a classic soap is often alkaline (high pH), while many modern cleansers use syndets (synthetic detergents) that can be formulated at a pH more compatible with the skin.

Studies have measured the pH of various liquid cleansers and lotions: many "soap-like" cleansers are in the very high pH range, while some syndets and "mild" cleansers are closer to skin pH.

Recent biophysical assessments also suggest that alkaline soaps can increase skin pH, water loss (TEWL) and erythema, while milder alternatives limit these effects.

The trap: "skin pH" is not enough to guarantee tolerance

There's a seductive idea: "If my cleanser has the same pH as the skin, it's bound to be gentle."

The literature clearly qualifies this point. An article dedicated to the role of pH in cleansing explains that a product can be at a "compatible" pH and still be irritating if its surfactant base is too aggressive, or if the formula is dominated by certain anionic surfactants under specific pH conditions.

In other words: pH is important, but it's not the only factor. Gentleness comes from the whole package: surfactants, lipid-replenishing agents, rinseability, fragrance and, of course, gesture (friction, duration, frequency).

How to recognize a cleanser that weakens your skin

Your skin tells you quickly. The most frequent signals are

• immediate tightness after rinsing,
• squeaky skin (sensation of lipid film being removed),
• systematic transient redness,
• increased sensitivity to normally well-tolerated skin care products.

The important point: if you change your cleanser and these signs diminish within a few days, it's often a sign that the previous cleanser was too stripping for your physiology.

A modern approach: effective cleansing without disrupting the barrier

Today's scientific logic is simple: effectively remove impurities (oxidized sebum, pollution, sunscreens, make-up) while minimizing :

• excessive dissolution of surface lipids,
• prolonged pH increase,
• repeated friction.

In practical terms, this often translates into more respectful textures and cleansing systems, and a stable routine: no need to "strip" to feel clean.

In the PERS approach: the aim of a soothing cleansing gel is precisely to purify without compromising skin integrity, especially if the skin is sensitive, dehydrated or reactive.

Key points to remember

• Skin has a naturally acidic pH, associated with a better barrier state and a more stable microbial balance.
• Repeated cleansing with a product that is too alkaline can increase skin pH and contribute to dryness, discomfort and reactivity.
• "Good pH" is not enough: the surfactant base, rinsability and gesture are just as important.
• Good cleansing leaves the skin supple, without tightness, and improves the tolerance of your routine over several weeks.

Scientific sources

• Lambers H et al. Natural skin surface pH is on average below 5, which is beneficial for its resident flora (2006).
• Thune P et al. The water barrier function of the skin in relation to skin surface pH (1988).
• Tarun J et al. Evaluation of pH of bathing soaps and shampoos for skin and hair care (2014).
• Kulthanan K et al. The pH of antiseptic cleansers (2014).
• Khosrowpour Z et al. Skin biophysical assessments of four types of soaps (2022).
• Ananthapadmanabhan KP et al. pH-induced alterations in stratum corneum properties (2003).
• Hawkins S et al. Role of pH in skin cleansing (2021).
• Mijaljica D et al. Skin Cleansing without or with Compromise: Soaps and Syndets (2022).