A study on the pH of commonly used soaps/cleansers available in the Indian market

Introduction

Considerable work has gone in the understanding of the relation of pH of the soaps and its effect on the skin. The general rule is that soap-based cleansers exhibit a higher pH than products based on synthetic detergents.

The skin′s surface is slightly acidic, giving rise to the concept of acid mantle. Intact skin exhibits an ability to recover from pH changes, even when exposed to highly alkaline materials although prolonged exposure to materials applied under occlusion may overwhelm the skin′s buffering capacity.

While some argue that the contact time of the cleanser with the skin is too little to cause significant change in pH, studies have proved other wise. Bechor et al[1] examined 41 marketed skin cleansing skin products and found that on an average, the skin surface pH increased by about 0.6 units after 30 seconds of washing and returned to the baseline within about 36 minutes. Even in the worst case, the surface pH was raised by 1.3 units and recovered within 90 minutes. Sauermann et al[2] reported that the skin′s surface pH recovered 2 hours after a 5-minute face wash with soap.

Korting et al[3] reported that skin surface pH recovered within several hours after a 2-minute wash of the forearm and forehead with soap. These authors also noted a small but persistent elevation in skin surface pH at both body sites over a 4-week use period involving twice daily, 2-minute washing with soap.

The impact of the alteration in the skin pH is clearly seen with the help of the study conducted by Korting et al.[3] The study demonstrated the effect of 2 cleansers, one at pH 5.5 and another at pH 8.5, on the resident bacterial flora of the skin. Subjects were asked to wash the forearm and the forehead with the 2 synthetic detergents at different pH levels. Neither of the cleansers affected the level of staphylococci on the forearm or the forehead. However, there were more Propionibacterium aches on the skin of the forehead at the end of the first week in the group using the alkaline synthetic cleanser.

The important conclusion drawn from this study was that preservation of the skin pH may be important to control the bacterial count on the skin surface in patients of acne.

In some studies it has been shown that the irritation potential of the cleanser is not related to the pH.[5] According to some, pH is an indicator of irritancy potential of a cleanser. They argue that, if the cleanser tends to change the pH of the skin, the stress on the skin buffering may alone cause irritation.[6]

The pH of a cleanser has an effect even on the moisture content of the skin. Gehring et al reported that a multi-component emulsion with a pH value of 7.5 had a greater drying effect on the skin than a similar emulsion with a pH of 4.5.[7]

Materials and Methods

Soaps commonly available and used by the public were taken for assessment of pH. They included the following categories of soaps-antibacterial, moisturizing, glycerin and sulphur containing, ayurvedic, baby soap, neem and lime containing, soaps sold as beauty bars, anti-acne face wash, routine bathing bar, dove bar soap, aquaderm and the new entrant into the ethical market cetapHil. Kindly note that all except, the anti-acne face wash, aquaderm and cetapHil were bar soaps.

The pH was determined with the help of litmus paper-Indikrom papers from Qualigens fine chemicals. In case of bar soaps, a few drops of tap water at room temperature, were poured onto the soap, rubbed to obtain lather and the litmus paper dipped into it where as in case of the liquid soaps, a few drops were poured on to the litmus paper. The colour change was then compared to the standard for determining the pH [Figure - 1]

A change of color to green and deep green, correlating with a pH of 7-9 was seen with most of the commonly used soaps. None of the soaps brought a color change to blue color relating with a pH of 9 and above by this method. Only dove bar, aquaderm and cetapHil did not change color, indicating that their pH was around 6 by this method.

Discussion

The soaps commonly recommended and used by the population at large have a pH, which is neutral to alkaline in most cases, ranging between 7 and 9. Only 3 cleansing agents (from amongst the ones tested) aquaderm, dove - an OTC product and cetapHil had a pH in keeping with the normal skin. Even the glycerin and baby soaps, which are the so-called mild soaps showed a neutral to alkaline pH.

From the evidence available, the pH of the skin changes depending on the pH of the cleanser used. This has a multifold impact on the skin in terms of the moisture content, the irritability and the bacterial flora.

Thus, before recommending a cleanser to a patient especially in case of dermatitic, sensitive and acne prone skin, due consideration to the pH of the cleanser needs to be given.