Tradition and innovation in skin cleansing

However, this is not the only required group of actions when today’s respect for the skin (which is now considered a protected environment) is taken into consideration. There has to be an absence of immediate and delayed irritation, care must be taken to protect the resident flora and barrier lipids, and rinsing has to be easy and thorough. One also has to maintain the skin pH, restore the normal TEWL (transepidermal water loss) values, achieve skin wellness and appearance in order to satisfy these key requisites. Providing pleasant sensory characteristics, not only immediately during cleansing, but also in the long term, are now essential requirements in daily hygiene practice. All these needs are quite rapidly changing the adopted ingredients and shaping the physical forms of modern cleansing products.

Solid cleansers

Fluid aqueous solutions of surfactants are the most common cosmetic tools used in skin detergents. They have partially replaced the wide market of traditional alkaline soaps, probably the most ancient cosmetic cleanser of human history. However, solid cleansers based on fatty acid salts are still sold in abundance. They provide easy use and just the right amount of surfactant that is necessary to form foam, and emulsify and dissolve the excess sebaceous materials on the skin surface. Their low cost is quite appealing and the fragrance is developed during treatment with water and massage.

Their foam amount is a clear signal of efficient lipids removal. Moreover, the quick disappearance of foam during rinsing (helped by the reaction of fatty anions with calcium and magnesium ions that are always present in tap water), provides the user with sufficient indications about the end point of the hygiene operations. This process causes only temporary lipid destruction by the surfactant action of the soap.

The residual traces of calcium and magnesium stearates, which precipitate onto the skin, leave a good skin feel and the “clean” perception of gently lubricated but non-oily skin. Moreover, metallic soaps perform a form of long-term emulsifying/adsorbing action on successive sebum secretions, which are quite useful in case of greasy skin. If water hardness is too high, their efficiency is strongly reduced and tub cleansing can become time consuming, however, despite this effect most performances are still maintained.

The problems that arise are mainly with those consumers who have dry and sensitive skin. These users do not always tolerate the pH modification induced by soaps and the long lasting (about three hours) consequent disruption of skin conditions and equilibrium. Irritation is a common consequence, mainly in cases of frequent use, where a decrease in the skin barrier reduction and subsequent skin dryness are the unavoidable effects.

Super-fatted soaps have partially solved these problems, but a revolution has taken place with the introduction and use of syndets. They are still solid systems but they foam more easily, are resistant to hard water (even to sea water) and the pH can be kept in the skin value range. The promise of a “neutral” pH is easily verified. They also cost more and are consumed at a higher rate than normal soaps, but they allow greater freedom in formulation and allow the incorporation of far more delicate additives. However, they lack an essential requisite. Their rinse-off time is quite long, as their water hardness resistance results in the need for extreme dilution with copious rinsing to achieve their removal.

The residual skin feel is completely different to that of soaps, frequently a slippery sensation is perceived along with a certain dryness because of the combination of the surfactants with the skin proteins. More modern “combars” (also called combibars) combine the use of synthetic tensioactives with fatty acids at neutral pH. These now seem to be the most advanced solution to solid forms of surfactant hygiene. Indeed a high degree of skin equilibrium is claimed and demonstrated, their mildness is quite good, and the residual feel on the skin is very similar to the velvety sensation produced by traditional soaps. Unlike the pure syndets there is no real possibility of using them on the hair. Modern forms, coming from China, have acquired fancy shapes: flower petals, fruits, toys, etc. The addition of vegetal flours has contributed to their skin mildness.

Aqueous fluids

With the appearance, in the fifties, of liquid surfactant solutions, things rapidly changed. They had the right fluidity for easy dosage, gave foam in abundance, were independent of water hardness, were quickly soluble in water and could be packed in practical containers to give only a few aspects of a successful mix, which is still roaring in the market. Since their launch, much of the original harshness has been reduced and corrected by the appearance of increasingly milder surfactants. The evolution of foam boosters has made product foam creamy and longer lasting and the pleasantness during use has been further maximised.

Perfumes are increasingly more sophisticated and they scent not only the bathroom, but more importantly the skin and the hair. They allow the consumer to achieve a bath full of luxurious foam, and make hair cleansing a one step operation that includes skin cleansing. Personalised and functionalised variants appeared: antidandruff, antibacterial, fluid hand “soaps”, shower gels and bath creams. In order to fuel a burgeoning market, more and more conjugations of the initial forms have appeared: bubble baths with suspended exfoliating and scrubbing particles, jumbo and family sizes, hanging tubes and pearlised fluids. The addition of conditioners has contributed to the restorative action of hair and skin, while hydrophilic polymers allow a reduction of the active ingredients without impairing the foam volume. Skin mildness is the new key word and the increasing trend to add substantive oils (intended as a way to restore the eliminated lipids with emollient ingredients and barrier improvers) has strongly improved the restorative effects.

Mildness has been increased by sugar derived surfactants, fuelled by the rediscovery of forgotten surfactants (e.g. sarcosinates, taurates, etc) and the use of specialised blends. But the deodorant effect was still insufficient, mainly when strong antibacterial actions could not be accepted for their secondary effects on resident flora and safety drawbacks. Recently, a zinc derivative of a traditional surfactant moiety (Zinc Coceth Sulfate) demonstrated a long lasting deodorant action and enhanced skin mildness. This is probably due to the precipitation of small amounts of zinc hydroxid e, a known soothing ingredient and a mild antibacterial agent, onto the skin surface during the dilution with tap water and the consequent increase in the pH of the solution. Combinations with Capryloyl Glutamate also demonstrated a synergic deodorant action, allowed the complete elimination of preservatives and antibacterial agents from the formula, while adding anti-dandruff effect to shampoos.

The new liquids: oil detergency

The concept of oil detergency was already in the mind of modern civilisation and has recently acquired an increasing importance. The combination of high amounts of oils with adequate emulsifiers and surfactants has given rise to oil detergents, where foam becomes a secondary element, which is acceptable in some cases where mildness must be maximised. In other cases, products do not foam but form white emulsions while diluted. Skin cleansing remains superficial, and does not greatly impair the skin barrier. Some sensory elements are lost, but others like skin evenness and softness after bath have appeared. Detergent emulsions are also one aspect of oil cleansing.

Two phase products

These product types appeared in the early 70s in the United States, and they have recently acquired importance in make-up remover formulae. The reason for their success is that they only require a low level of emulsifiers although they do require shaking in order to obtain a nonpermanent emulsion that quickly breaks down and returns to two layers. Eye tolerability is also maximised.

“Mud” cleansing

On the wave of the cellulite treatments with thermal mud, cleansing foaming mud products have appeared. The application operation immediately recalls a childhood game, but cleansing is quite satisfactory and the skin is thoroughly cleaned with the clay particles exerting a “polishing” action to leave a residual feel that is very velvety and soft. So-called slimming agents can be added and the rinse-off performance resembles a purification rite, from the grey mud to the body’s clean skin. The residual clay also cuts down the excessive skin oiliness.

Bath salts

In this case, mild washing performances are obtained by decreasing the water hardness by forming a complex with anions and polyanions. The elimination of fats from the skin is low, but the high osmotic pressure experienced during the bathing process exerts a positive message on cell metabolism, as it is followed by a progressive return to physiologic equilibrium during rinsing. Recently pearlshaped bath crystals have appeared. More a propitiatory rite than a deep cleansing, it exerts beneficial effects through the abundant use of aromatherapy scents.

Bath tablets

In the age of multi-faceted perceptions during the use of cosmetics, cleansing has updated its performance by combining compacting technology with modern ingredients. We have now large compressed tablets and balls that quickly dissolve in the tap water to form lovely bubbles of carbon dioxide that release fragrance, make an appealing “sparkling” noise, colour the water mass and provide restorative ingredients to the skin. There are also liquids that are encapsulated into gelatine spheres, which release (after dissolution) emollient oils and mild emulsifiers that are a way to provide an even more luxurious and attractive experience for body cleansing.

Aerosol foams

One has to consider the reason for expending energy in foam formation when gas expansion could do the same job. The aerosol foams do not only apply to shaving, but are an enticing form of ready-to-use detergency.

The marketing of these attractive forms is quite appealing, especially when the container is transparent and a coloured mobile liquid instantly becomes gorgeous white foam when the container is actuated. The only limit is that propellants and metallic or glass cans make the combination expensive and short-lasting. Environmental protection is the new buzz word, so in these cases it would be better to use air together with a novel mixing device to produce foams. No-gas aerosol foams have been launched on the market that work by pumping an aqueous fluid through a suitable mesh where air is homogenously entrapped and a soft foam appears. Although these actuators are not cheap, the concentration of surfactants that is necessary to obtain suitable foam is very low, but which still have interesting advantages for the environment and the skin of the consumer.

The future of cleansing

The way to maximum skin mildness is two sided, either through the route of high technology or via vegetal ingredients. Gemini surfactants by virtue of their high efficiency are going to reduce, by at least ten times, the required amounts of surfactant. On the other hand, vegetal flours, rich in amphiphilic proteins, lipophilic vegetal oils and hydrophilic chains will introduce the skin-deep detergency without foam, because is based on the adsorption mechanism of excess skin lipids and debris. Will vegetal saponins increase the importance of renewables sources? Will biotechnologically adapted bacteria produce new fully degradable surfactants? These ingredients are already being mentioned in the literature. Big surprises wait for us under the next shower.