Le savon de Marseille est-il vraiment à pH neutre ?

Many users wonder if the Marseille soap they cherish is truly a pH neutral product. The truth lies in understanding the chemistry behind this traditional soap, its soap composition, and how its pH level interacts with different skin types. With the soap market flooded by various products claiming gentle and natural properties, it becomes crucial to discern whether Marseille soap fits the profile of a hypoallergenic, skin-friendly cleanser or if its alkalinity might pose challenges.

Authentic Marseille soap is known for its simple and natural ingredients, primarily composed of vegetable oils such as olive oil and sometimes coconut oil, combined with sodium hydroxide through a chemical reaction called saponification. This process results in a solid soap bar valued for its environmental benefits and cleaning efficiency. However, this traditional process yields a distinctly alkaline soap with a pH level typically between 9 and 10, which is considerably more basic than the skin’s natural pH.

For skin care, this distinction is significant. The skin’s surface thrives in a mildly acidic environment, averaging a pH near 4.7, which supports its barrier function and microbial balance. In contrast, an alkaline soap such as Marseille can disrupt this balance, particularly for sensitive, dry, or mature skin. Recognizing these aspects enables users to make informed choices about when and how to include Marseille soap in their routines without compromising skin comfort.

What Is the Real pH Level of Marseille Soap and Why It Matters

The genuine Marseille soap maintains an alkaline soap status with a pH level generally ranging from 9 to 10. This derives from the absence of acidifying agents in its formula and the classical production process—cooking oils with sodium hydroxide, followed by multiple washings and curing. The soap properties that emerge include potent degreasing capabilities and efficient cleansing, making it a favored product for hands and body.

However, it is crucial to understand that a pH neutral soap, which would have a value of 7, is fundamentally different. Such soaps are often syndets—sythetic detergents rather than true soaps—and have formulas designed to better match the skin’s natural acidity.

Impacts of Alkaline pH on Skin Health

The skin’s acid mantle serves as a natural defense against irritants and pathogens. When exposed to a soap with a high pH, the skin’s surface temporarily becomes more alkaline, which can lead to depletion of lipids and disruption of the microbiome. This results in sensations of dryness, tightness, or even irritation, especially after frequent or prolonged washing.

Nonetheless, this effect varies according to individual skin types. People with normal or oily skin often tolerate Marseille soap well, appreciating its thorough washing and lack of synthetic fragrances or harsh additives. Conversely, those with sensitive, atopic, or mature skin may find the soap too aggressive for facial cleansing or daily use.

Variability in Marseille Soap’s pH and What Influences It

Several factors can induce minor variations in the pH level of Marseille soap bars. These include:

• The proportion of olive oil versus harder oils like coconut oil.
• The duration and number of washing steps (relargage process) during production.
• The local water hardness and environmental conditions during curing.
• Additions such as surplus oils in “surgras” formulas that aim to improve moisturizing properties.

While these elements influence the perceived gentleness and slight pH shifts, they do not render the soap pH neutral. Instead, they moderate the alkalinity, enhancing comfort post-rinse.

Comparison of Marseille Soap with Other Cleansers by pH and Use

Type of Cleanser	Base	Typical pH	Best for	Characteristics
Marseille Soap	True soap (fatty acid salts)	9–10	Body, hands, heavy-duty cleaning	Natural, effective degreasing, may dry sensitive skin
Alep Soap	Olive and laurel oils	~9	Body, tolerant facial skin	Gentler, varies with laurel percentage
Syndet (facial cleanser)	Soft surfactants	5–5.5	Sensitive or reactive skin	Maintains skin pH balance
Glycerin Soap	True soap with glycerin	8–9	Normal to dry skin	More moisturizing than dry soaps
Conventional Shower Gel	Surfactants + additives	5–6	General family use	Varies with formula and fragrances

Using Marseille Soap in Your Skin Care Routine Without Disruption

To maintain skin comfort when using alkaline soap, consider the following recommendations:

• Limit use on the face, especially for sensitive or dry skin types.
• Prefer lukewarm water and shorten contact time to minimize disruption of the skin barrier.
• Rinse thoroughly to reduce residue that may contribute to dryness.
• Apply a moisturizer immediately after washing to restore hydration and preserve the acid mantle.
• Alternate with syndet cleansers when possible to maintain skin balance.

Particularly for hands and body, Marseille soap remains a practical choice, balancing traditional natural ingredients with effective cleansing, provided it is used with awareness of its alkaline nature.

Can Marseille Soap Be Used on Hair?

Hair generally prefers acidic products for maintaining the cuticle integrity. Regular use of Marseille soap may cause the hair shaft to swell and cuticles to open, leading to dryness and frizz. If employed occasionally, following up with an acidic rinse such as apple cider vinegar helps smooth the hair surface.

Is Marseille soap truly pH neutral?

No. Authentic Marseille soap is alkaline, with a pH between 9 and 10, significantly above the neutral pH of 7. True pH neutral cleansers are usually syndets or specially formulated products.

Can Marseille soap cause skin irritation?

Yes, especially if used frequently on sensitive or dry skin, due to its high pH disrupting the skin barrier and drying out the skin.

What types of skin benefit most from Marseille soap?

People with normal to oily skin and those needing effective degreasing may find it suitable, mainly for hand and body cleansing.

How can I measure the pH of Marseille soap at home?

Dissolve 1 g of grated soap in 99 g of distilled water, stir, wait 30 minutes, then use pH strips or a calibrated pH meter for measurement.

Are there alternatives to Marseille soap for sensitive facial skin?

Yes, syndet cleansers with a pH around 5–5.5, offered by brands like La Roche-Posay or Avène, are more suitable for maintaining a healthy skin barrier.