An expansion in the range of products designed to cleanse the skin or hair in natural cosmetics has been observed in recent years. "Less foaming", "less cleansing", "less effective"... however, these less than flattering terms are often used to describe these cleaning products. In response to this phenomenon, the question of the importance of foam in these everyday products compared to conventional products has been raised. In this article, let's discuss how this foam is formed and whether it plays a specific role?
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Shampoo, shower gel, facial cleanser... why do cleansing products foam?
Summary
Published August 11, 2023,
updated on October 3, 2024,
by
Stéphanie, PhD, Doctorate in Life and Health Sciences
—
4 min read
Cleansing Products: Where Does the Foam Come From?
As water alone is not sufficient to remove the oily dirt from everyday life that has accumulated on the scalp and skin, cleaning products, regardless of their formulation, contain cleansing agents known as surfactants. These amphiphilic molecules, responsible for cleaning, are polarized with a hydrophilic head that has an affinity for water and a lipophilic tail that has an affinity for fats. Thus, they can attach to both water and fats, and effectively remove dirt present on the hair or skin during rinsing.
They are also the ones who create the foam. During hair washing or skin cleansing, as you massage your scalp or rub your skin, small air bubbles form, a result of an emulsion between water, dirt, and surfactants. Indeed, these bubbles form when air molecules agitate and come into contact with the diluted product. Without external action, these air bubbles are unstable and burst quickly. However, with the action of surfactants, the air bubbles are encapsulated and stabilized, creating abundant foam.
A Connection Between Foam and Cleansing Power?
"The more it foams, the better it cleans."
We often associate abundant foam with high performance/efficiency, especially when we notice that a conventional shampoo foams more when the hair is clean. However, the amount of foam produced does not correlate with its ability to cleanse, even though in absolute terms, the more a product foams, the more it cleanses.
Indeed, it is not because a shampoo lathers a lot that it cleans well. The foam is one of the effects of the presence of surfactants. It is not a cleansing agent and is not proof of effectiveness. Therefore, it is possible to have an effective shampoo with little foam or the opposite with a shampoo that produces a lot of foam but cleans less effectively.
The volume of foam produced depends on the type of surfactant used. These are typically sulfated surfactants (e.g., sodium laureth sulfate, sodium lauryl sulfate, ammonium lauryl sulfate, etc.) that have this property of producing a generous foam. However, the more generous the foam, the greater the risk of skin drying out. Indeed, they have a tendency to weaken the skin's protective hydrolipidic film, making it more reactive and irritable.
On the other hand, criticisms are leveled at "natural" shampoos, which are sulfate-free and use non-ionic or amphoteric surfactants derived from plant extracts (e.g., coco-glucoside, decyl glucoside, lauryl glucoside, sodium cocoyl glutamate, disodium cocoyl glutamate, sodium lauroyl glutamate, etc.), for producing less foam. However, these cleansing agents are gentler on the skin.
Nevertheless, foam is not without its uses. It plays a role in the practicality of cleansing products. It facilitates the distribution of the product on the skin, the scalp, between hair fibers, and along strands, ensuring a thorough cleaning and avoiding excessive rubbing. This is an indicator that can be particularly useful for thick hair or hair with high density. Moreover, it also helps to use a reduced amount of product. To put it simply, a voluminous foam actually indicates that there is nothing left to clean, that there are no more impurities to remove.
Note : A shower gel or a facial cleanser will contain between 10 and 12% of surfactants in its formula, while a shampoo will have between 15 - 20% of surfactants, which is why a shampoo will foam more.
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