What's the Difference Between a Conventional Soap and a Dermatological Bar?

Gentle natural surfactants derived from oils and fats like salts of fatty acids are present in traditional soaps. These oils act as the base surfactant in soap, and their main function is trapping oils and dirt from the skin in the foam, which can be rinsed away after. Soap ingredients include vegetable or animal oils, caustic soda, foaming agents, fragrances and colorants. However, some combinations of surfactants and other ingredients may be unsuitable for sensitive or compromised skin, often leading to dryness and irritation. 

Syndets, on the other hand, are manufactured using a selected range of materials that are compatible with keeping the skin’s structure and function intact. This formulation includes synthetic surfactants derived from petroleum-based or plant-based raw materials like sodium cocoyl isethionate or sodium lauryl sulfate (SLS). In most cases, they tend to have a pH-balanced formulation and may lack any fragrance or harsh additives, which makes them more skin-friendly compared to conventional soap. Syndet formulation usually includes vegetable oils, glycerine, vegetable butter and plant extracts (chamomile, aloe vera, etc.)

The most pronounced difference between the two categories lies in the pH levels. Traditional soaps are strongly alkaline, with pH levels between 8.5 and 11.0, which interferes with the skin barrier and promotes dryness or irritation. An alkaline pH affects the skin barrier because it alters the naturally existing acid mantle of the skin, which is slightly acidic and works as a defense mechanism against bacteria and dryness possible. Prolonged exposure to alkaline substances weakens the acid mantle, leaving the skin dry, irritated, and more susceptible to infection. Further, high pH can injure the lipids and enzymes of the skin-tightening response to moisture retention. Syndets are designed to lie in the neutral to mildly acidic range (5.5 - 7.0), which is closer to the skin pH - this helps with restoring the skin's barrier function and minimizing chances of irritation.

A comparative study was performed by PAYE & al. (2001) in order to evaluate the predictive value of patch testing for assessing the skin irritation potential of body-cleansing products compared to the products' normal use at home. The study was held double blind for 10 weeks and involved 50 healthy female volunteers; half were given an alkaline soap bar, the other half a syndet dermatological bar. Skin reactions were assessed clinically through visual examination and chemical measurements. Meanwhile, subjects kept records of dryness, tightness, and irritancy. The results showed no remarkable changes, except for a slight increase in pH for the alkaline soap bar, which was perceived as more irritating by the users. Soap chamber tests confirmed that the soap bar had higher irritancy than the syndet bar. The results suggest that patch testing does not reliably predict irritancy under normal conditions of use, though the soap chamber results are very close to consumer perception of product irritancy.

Both soap and syndets contain amphipathic molecules (hydrophilic head and hydrophobic tails) that help in washing action. The difference lies in the surfactant composition: soaps mainly consist of anionic surfactants such as sodium laurate or sodium oleate. While effective, these surfactants may cause skin irritation. In contrast, syndets employ surfactants such as non-ionic, anionic, cationic, and amphoteric combinations that increase cleansing power while ensuring skin compatibility. Sodium alkyl isethionate is a typical syndet surfactant, with low irritation when compared to conventional soaps.

Many conventional soaps are produced using animal fat (surgras soaps can be an exception). Some alternatives use biosurfactants derived from plants or microorganisms; however, these are not widespread in usage. With respect to sustainability, even synthetic detergents have more viable options. A majority of the newer dermatological bars use biosurfactants from renewables, which have a smaller environmental impact and improved biodegradability. Additionally, the synthetic detergents keep stability to a large extent at varied pH and temperature ranges, which makes them suitable for long-term applications.

While traditional soaps are centuries old and still used by many, dermatological bars or syndets present a much better option, particularly for those with sensitive skin. Syndets are designed to be pH-balanced, gentle, and more suited to maintaining skin health with little irritation. Further, their sourcing is sustainable, providing further environmental benefits, which is another reason why they are the preferred option in personal care.