By adding one or even a number of different preservatives listed in the German Cosmetic Decree (Kosmetikverordnung - KVO) the microbiological stability can be assured. There is, however, a disadvantage: there is virtually no exception to the fact that the substances listed may cause sensitizations (allergies) under certain conditions.
In terms of consumer protection, there are several important alternatives: bottling under sterile conditions, avoiding the addition of water (e.g. oleogels, oils), hypertonic water phases (high osmotic pressure due to high substance concentrations in the aqueous phase) or by adding substances containing hydroxyl groups. These alternatives are sufficiently documented in technical literature, but regarding the production costs, they are far more expensive than processes including preservatives according to the German Cosmetic Decree list. This is the reason why the above mentioned processes are rather rarely applied by the cosmetic manufacturers.
Hydroxyl group containing substances are, among others: ethanol (alcohol), propylene glycol, glycerine, pentanediol, sorbitol and the monosaccharides. With the exception of ethanol, all the substances mentioned increase the skin hydration, hence they are multifunctional substances. Consequently, the definition of preservatives according to § 3a, section (1) of the German Cosmetic Decree is not applicable and cosmetic products containing these substances can be declared "free of preservatives" apart from the fact that in contrast to the substances listed in the German Cosmetic Decree, sensitizations can virtually be excluded.