Saponins - vegetable soaps in cosmetics?

What are saponins?

Saponins are phytochemicals found in all higher plants. The name derives from the lat. Sapo - soap. They are due to many possible carbohydrate structures as a variety of substances before^[1].

What are saponins chemically?

Fig. 1 The structural formula of gypsogenin, a triterpene saponin. It comes u.a. in soapwort.

Saponins are glucosides (sugar esters) of steroids, steroid alkaloids (nitrogenous steroids) or triterpenes. They can be divided into a large number of subcategories, with many analogues possible due to a wide variety of backbones, sugars and ester positions^[2].

What are their properties?

The saponins are abundant in higher plant species, e.g. in soy, chickpeas, peanuts, spinach, tea, ginseng and quinoa. They are called saponins because of their ability to form stable foams when shaken with water. These foams show modes of action similar to those of detergents. They serve plants as protection against predators and fungal infestation. They also affect membrane permeability (cell permeability) and complex (bind) cholesterol. In addition, they have hemolytic activity, ie the ability to red blood cells to solve and possibly destroy. They also have fortifying, anti-inflammatory and hormone-stimulating properties. Due to their ability to dissolve red blood cells, they must not enter the blood^[3].

What are their applications?

Saponins have long been used as a detergent, and even as a moderate cure for syphilis. Nowadays they are used as auxiliaries, as so-called QS-21, in medicine. QS-21 enhances the response of the immune system to antigens, and is obtained from Quillaja^[4].

What do saponins do in cosmetics?

In der Kosmetik werden Saponine als Biotenside und Schaumbildner benutzt. So finden sie in Naturshampoos Anwendung. Oftmals werden Soja Saponine verwendet, aber auch Quillaja (Quinoa) Saponine werden eingesetzt. Sie wurden eine lange Zeit ignoriert, da man befürchtete, dass sie aufgrund ihrer hämolytischen Aktivität für Reizungen sorgen würden. Nun werde sie jedoch genau für das Gegenteil, also sehr empfindliche Haut, eingesetzt, so z.B. für Augen und Dekolletee^[5].

Bio Shampoo

Sources:

Wikipedia^[2][3][4]

Report on saponins in cosmetics^[1][5]

Image sources: Wikimedia Commons, Flickr. The image rights go to the owners of the images.