"That which does not kill us makes us stronger. " This reflection from Nietzsche could almost be applied to the hormesis concept. The term was first introduced in 1943 [1] to describe a dynamic property of the living "high concentrations of toxic substances inhibit whereas low concentrations stimulate."

Regularly repeated micro-stresses

Everything is a question of dosage and regularity. It is important to know the limit beyond which stress whether physical, biological or chemical applied to a body no longer exerts a stimulating effect but a deleterious one. In practice and in everyday life, where the phenomenon of hormesis is evident is during physical activities  [2]. As part of a regular and moderate practice of sport, substances produced by the body (free radicals, acids, aldehydes) will generate beneficial reactions, while these same substances can be harmful in high concentrations.

This principle can also be found in calorie restriction or with the application of low ionizing radiations. It has been demonstrated  [3] that the frequencies of chromosome breaks induced by waves were lower when cells were treated before with very low doses and even more so when a few hours separated the two irradiations. The regular repetition of low stresses allows the cell or even the whole organism to better resist a stronger stimulation.

Studies conducted on cellular aging

In the field of cellular aging, Prof. Suresh Rattan [4] is one of the pioneers in the development and use of the hormesis concept. He highlighted the hormétines, a class of natural and synthetic compounds that ensure a slowdown in the ageing process. Studies (5) were conducted on cell cultures to measure the impact of micro stresses regularly applied like as a temperature of 41°C during 1 hour two times a week or 50µM of rosmarinic acid or 0.25µM of curcumin. Responses show a strengthening of cell functions and a global anti-aging effect.

All the explanatory mechanisms are not elucidated yet, but these micro solicitations could, result in the increased expression of some repair enzymes, enable the production of resistance proteins such as the HSPs, stimulate the proteasome activity, improve the sodium/potassium pump rate, and play a role in the expression of certain genes related to aging.

Applications in cosmetics

It is on the basis of the work of Suresh Rattan that Givenchy launched in 2010 VAX’IN for youth, the first cosmetic product enriched with a complex of active ingredients made from Sanchi and hypotaurine, two hormétines which are likely to reproduce the hormesis phenomenon. By generating micro stimuli, skin cells produce in doses in proportion to their need, their own resistance protein to aging, the HSP70. In vitro tests show a 24% increase in its synthesis. Cells defence and repair mechanisms are reinforced, the skin resistance to the signs of aging is increased. An instrumental test performed on several women whose skin was subjected to aggressive washes showed a 30% improvement of the skin protection.

This year, Givenchy has made another addition to the range VAX’IN for youth with a version specifically dedicated to the sensitive area around the eye.

New ingredients that mimic hormesis

On the ingredient marketplace, it is Sederma who paved the way for a broader use of hormesis in cosmetics, with Resistem™, an anti-aging active derived from plant cell cultures. This year, Silab followed suit with Vitagenyl®

These compounds reproduce the hormesis phenomenon leading to an increase in the cells defence capabilities. Resistem™ helps in particular fight against noci-products. Tested in vitro on keratinocytes stressed with hydrogen peroxide, a strong inhibition of intracellular peroxides was observed (-88% compared to control). The proteasome activity on the hydrogen peroxide stressed fibroblasts is also stimulated (+57% compared to control). Moreover, cellular longevity is increased with a 74% increase of the sirtuin-1 synthesis and tissue regeneration is boosted. It is the "bodyguard" of the skin, helping, through a virtuous circle to regain its natural beauty.

"To develop this product, we inspired ourselves with the work of Prof. Rattan who published a hormetic response profile corresponding to several characteristics of cellular survival and repair, Resistem™ demonstrates very good results on all criteria," confirmed Olga Gracioso in charge of marketing and communication for Sederma.

For its part, Vitageny®, with a rich content in purified alpha-glucans obtained from peach leaves, stimulates the expression of Vitagènes involved in cellular homeostasis and coding such stress resistant proteins as the HSPs, the thorédoxine and sirtuin-1. Tested in-vitro at 1%, Vitagenyl® stimulates the viability of fibroblasts in nutrient deficient medium and their proliferative capacity. Vitagenyl® through its hormetic action helps cells be better prepared and equipped to combat against external aggressions. Vitagenyl® improves the regenerating potential and vitality of the skin.

Both active are positioned as anti-aging and offer, in the wake of VAX’IN for youth, promising prospects for the use of the hormesis concept in cosmetics.