Cleansing bars are a popular form of cleanser, but they can differ significantly in their composition and their effects on skin health. The two main types are soap-based bars and synthetic detergent (syndet) bars. Understanding the differences between these can help individuals choose the most appropriate product for their skin, particularly for those with specific skin concerns.
Traditional soap bars are typically made by the saponification of natural oils or fats with a strong alkali, such as sodium or potassium hydroxide. This process creates salts of fatty acids, which are the main cleansing agents in soap. A key characteristic of soap is its alkaline pH, typically ranging from 9 to 11. This high pH can disrupt the skin’s natural acidic mantle, which is crucial for maintaining the skin barrier function, preventing the growth of harmful bacteria, and regulating enzyme activity in the stratum corneum.
When used to cleanse the skin, soap can remove not only dirt and oil but also essential skin lipids, including ceramides, cholesterol, and fatty acids. This can lead to a compromised skin barrier, increased transepidermal water loss (TEWL), dryness, and irritation. Individuals with sensitive skin, dry skin, or conditions like eczema and atopic dermatitis are particularly susceptible to the negative effects of soap due to their already compromised barrier function. Studies have shown that washing with soap can increase stratum corneum stiffness and induce dryness compared to syndet bars.
Syndet bars, on the other hand, are formulated using synthetic surfactants (surface-active agents) that are typically milder and have a pH closer to that of the skin (around 5.5 to 7). These surfactants are designed to cleanse effectively while being less disruptive to the skin barrier. Syndet bars often contain a blend of different surfactants, as well as other ingredients like moisturisers, emollients, and humectants, to further mitigate potential dryness and irritation.
The milder pH of syndet bars helps to preserve the skin’s acidic mantle and is less likely to disrupt the lipid matrix of the stratum corneum. As a result, syndet bars generally cause less dryness, irritation, and barrier disruption compared to soap bars. Clinical trials have demonstrated that switching from soap to syndet bars can lead to improvements in skin texture, brightness, clarity, and tone, even in individuals with photodamaged skin. Syndet bars are also often better tolerated by individuals with sensitive skin and skin conditions like acne, rosacea, and atopic dermatitis, where maintaining barrier integrity is crucial.
Another difference lies in the potential for residue left on the skin. Soap scum, which is formed when soap reacts with minerals in hard water, can leave a film on the skin that may be irritating for some individuals. Syndet bars are less likely to form such residue.
However, not all cleansing bars, including syndet bars, are created equal. The specific surfactants and other ingredients used in a syndet bar can influence its mildness and overall effect on the skin. Some syndets can still be somewhat stripping, although generally less so than traditional soap. It is important to choose syndet bars that are specifically formulated for sensitive or dry skin if these are concerns. In summary, while both soap-based and syndet cleansing bars serve the purpose of cleansing the skin, syndet bars are generally considered milder and less damaging to the skin barrier due to their more skin-friendly pH and less stripping surfactant systems. For most individuals, and especially those with sensitive skin or skin conditions, syndet bars are often the preferred choice for maintaining skin health and minimising the risk of dryness and irritation associated with cleansing.