The water activity measurement, a key indicator to evaluate the self preservation of cosmetic products

Micromer, the subsidiary of IDEA group in charge of microbiology activities, has just acquired an “Aw-meter”, which enables to measure the water activity, one of the major parameter influencing the preserving of cosmetic products. Sophie Corre, PhD, head of Micromer, tells us more:

“The water represents the largest component in most food, pharmaceutical and cosmetic products. The activity of water (Aw) is a notion introduced in the Twenties by Levis and Randall to measure the bioavailability of water for biological reactions.

Actually, the micro-organisms (bacteria or fungi) needs “free” water or available water to develop themselves. But be careful, the water activity doesn’t represent the water content but the water availability. This activity of water is measurable by an Aw-meter and is between 0 and 1. The more the water activiy is high, the more the quantity of free water is big and the more the micro-organisms develop themselves. The majority of bacteria need a water activity ≥0.90 to grow, though most deterioration moulds multiply themselves from 0.60.

Thus, this water activiy is one of the main parameter influencing the product’s preservation. Already widely used in the food-processing industry, it is also a notion more and more used in the cosmetic area. Thus, it is one of the parameters taken in reference in the NF ISO 29621 standard (July 2010) from the “risk appreciation and cosmetic products at low microbiological risk identification guidelines”.

According to this standard, the products having an Aw ≤ 0.75 would be at low microbiological risk. Lips balms, lipsticks, blushes (…) enter in that category. However, we should point out that this notion of product at low microbiological risk can’t be based on only one parameter and depends on a multi factors analysis, in taking into account physicochemical parameters linked to the product (pH, nutritive substances or hostile substances content), parameters linked to the manufacture environment (temperature of manufacture, temperature of filling, type of packaging…) and parameters linked to product’s conditions of use (PAO…).”