Natural cosmetics: All you need to know: COSSMA

Cosmetic products have a very long history and were part of life in ancient Egypt, Greece and Rome. A broad spectrum of cosmetic actives and formulations such as ointments was available, for example cold cream of Galen of Pergamon (Roman doctor) consisting of rose water, olive oil and beeswax. Cosmetic formulations were also applied in the Middle Ages. Nostradamus (1503–1566) condemned cosmetics in Christian Europe as materials for heathens. He presented the following cosmetic recipe: „Powder to clean the teeth and to make them whited and a flavour some breath in just few days …“. In Islamic countries fragrances and cosmetic perfumes were used.

In recent years, intensive developments have been realised in research, marketing and commerce to generate natural cosmetic products. In 2001, the German Federal Ministry of Health presented the following definition covering both natural cosmetic actives and excipients: „Natural cosmetics are products prepared only from natural materials. Natural materials are substances from herbal, animal and mineral sources. Only physical methods can be used for the preparation/production including extraction by use of water ethanol, glycerine or carbon dioxide.“

These are the advantages of natural cosmetic actives:

Natural actives are often mixtures (their effects are not due a single compound).
In general, they have a very good physiological compatibility and additional natural compounds such as tannins improve the properties such as the solubility in formulations and penetration into the skin.

These are the challenges confronting natural cosmetics:

Standardisation of cultivation (controlled farming), year to year content of the cosmetic actives.
Standardisation of raw materials (actives of the plants and of the extracts).
The differences between natural actives and excipients and the semisynthetic ones have to be strictly taken into account.

The challenge of developing plant-based surfactants

The challenge in the field of natural cosmetics is the development of natural surfactants as surfactants are the main constituents of a cosmetic formulation in terms of physical stability.

In cosmetics, there is a broad spectrum of semi-synthetic surfactants commercially available. The challenge here, however, is to develop plant-based surfactants. The portfolio merely comprises lecithins/phospholipids, wheat protein hydrolysates, and biosurfactants such as lipopeptides.

Natural lecithins (phospholipids, PL) consist of the same components (see fig. 1*). The main constituent is phosphatidylcholine (PC). PL have amphiphilic properties because of their hydrophilic head group and their lipophilic tail. The relevant PL shown in fig. 1* include phosphatidylethanolamine, phosphatidylserine and phosphatidylcholine. The origins of plant-based PL are soya, sunflower and rapeseed.

Lecithins/PL which are very mild surfactants are widely used both in cosmetics and in pharmaceuticals for suspensions, liposomes, mixed micelles and emulsions (see fig. 2).

fig. 2: Light microscopic image of an O/W emulsion with lecithin as emulsifier. Photo: University Halle-Wittenberg

Phytoceramides – natural barrier stabilisers

The human stratum corneum (SC) consists of corneocytes (dead cells) which are embedded in a highly structured lipid matrix. The SC lipids are very important for the barrier function of the human skin. The SC lipids are composed of nearly equimolar quantities of ceramides (CER), cholesterol, and free fatty acids. The CER appear to be the main SC lipid class.

Phytoceramides (phytoCER) are glycolised in plants. However, the structure of the hydrolysed phytoceramides is similar to the human SC CER (see fig. 31, 2*). PhytoCER have 3 or 4 OH groups in their headgroups, just like the human SC CER. Therefore, phytoCER can be used as natural cosmetic actives for purposes such as:

prevention of skin diseases such as atopic dermatitis and psoriasis
products for aged skin
repair of defective skin barrier and dryness due to depletion of SC CERs
lipid replacement therapy when additional exogenous CERs are needed
recovery of the skin barrier function
skin hydration and retention of skin moisture

With the help of neutron scattering it was shown that phytoCER from Ethiopian plants, particularly from Ethiopian oat, form very stable bilayers similar to human SC CER such as CER NP and AP. Bilayer thickness measured of the CER AP and NP amounted to 4.48±0.01 nm and 4.99±0.01 nm for the phytoCERs from Ethiopian oat.

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