With countless soaps available on the market, it can be confusing to decide which one is best for your skin. Rashmi Rajpal, B. Tech in Cosmetology, explains the three main categories of soap, their chemical composition, and how they affect the skin.
pH stands for potential hydrogen, which indicates how acidic or alkaline a substance is. On a scale of 0 to 14, values below 7 are acidic, 7 is neutral, and above 7 is alkaline. The skin also has a pH, which reflects this balance and plays a crucial role in maintaining its health. 1
The ideal pH for adult skin is around 5.5, which means it is slightly acidic. This mild acidity helps preserve the skin's natural oils and protects against harmful bacteria. When skin pH shifts too far in either direction, it can disrupt the skin barrier and its natural microbiome.
The first category is toilet soap. Rashmi explains, “All the categories of Toilet Soap are made through an alkaline process. First, a cheap oil is taken and 50% alkaline solution is added to it. That is, the pH of Sodium Hydroxide and Potassium Hydroxide is 9 onwards. It can even go up to 11.”
Toilet soaps are measured by Total Fatty Matter (TFM), which reflects the percentage of fatty acids in the soap. A higher TFM indicates better hydration, while low TFM may leave excess alkali, potentially irritating the skin. Frequent use of highly alkaline soaps can disrupt the skin barrier and increase transepidermal water loss, so moisturizing afterward is essential. Rashmi advises, “If you are still using it, then please don’t forget to moisturize your skin.”
The second type of soap is glycerin or handmade soaps, which are milder on the skin. Rashmi states, “Their TFM is 35–40%, but they are super hydrating for the skin. And only 10–20% alkaline solution is added to them. Their pH is from neutral to slightly alkaline, but they do not rupture the skin barrier.”
Because of their lower alkalinity and higher glycerin content, these soaps are suitable for dry or sensitive skin. Research supports that soaps with moderate TFM and lower pH reduce barrier disruption and maintain skin hydration, making them a healthier choice for daily cleansing.
The third category includes syndet bars, also called synthetic detergent or beauty bars. Rashmi explains, “They don’t have any TFM, but they are made from surfactants. It’s like converting sulphate-free shampoo into a bar. They are very safe for our skin.”
Syndets are pH-balanced, usually around 5–6, which aligns with the skin’s natural acidity. Studies show that syndet bars minimize irritation, preserve the skin barrier, and prevent excessive water loss. These features make them ideal for frequent handwashing and for people with sensitive skin.
An imbalance in skin pH can lead to several problems. Dryness and flakiness can occur because natural oils are stripped away. Acne may develop as harmful bacteria find a more favorable environment. Skin may also become red, itchy, or inflamed, increasing sensitivity.
It is difficult to measure skin pH accurately at home. Dermatologists recommend gentle, pH-balanced cleansers instead of highly alkaline soaps. Products designed for sensitive skin are generally safer and help maintain natural acidity. Consulting a dermatologist can help determine the right skincare routine to restore and maintain balanced skin pH. 1
Rashmi Rajpal summarizes, “Now you select which soap you should use.” The choice depends on skin type, frequency of washing, and sensitivity:
Toilet soaps: Provide deep cleansing but require moisturization afterward.
Glycerin or handmade soaps: Offer hydration and gentle cleansing for daily use.
Syndet bars: Ideal for sensitive skin and frequent washing.
Understanding TFM, pH, and formulation can help consumers make informed choices that maintain healthy, balanced skin.
Reference:
Cleveland Clinic. “What Is Your Skin’s pH and Why Does It Matter?” Health Essentials, June 29, 2023. https://health.clevelandclinic.org/what-is-skin-ph.
(Rh/ARC/MSM)