The use of the word ''antimicrobial'' preservative raises the need to define exactly what s kind of activity is needed for a preservative. What are the organisms of concern: bacteria, fungi, viruses, or even spores? The scale of the activity spectrum is based on almost three parameters: (1) the survival, or even multiplication, of particular organisms in a wide range of products; (2) the pathogenicity of these organisms by the route of administration; and (3) the possibility to find effective chemicals at nontoxic concentrations.
Sporicidal action must not be considered because sporicidal chemicals are very rare (e.g., aldehydes are too toxic to be used in a cosmetic product at effective concentrations). Moreover, infectious problems induced by spore formers are very seldom, as previously discussed for the talcum powder in this chapter. Even if aerobic spore formers are often found in raw materials and finished products, according to Davis  they should not be a hazard to human health.
Virucidal action is not considered for cosmetics. These facts restrict the spectrum of a cosmetic preservative to bacteria and fungi. According to the most widespread opinion, a bactericidal and a fungicidal effect is needed so that the contaminating organisms accidentally introduced in the preparation will be killed. A bacteriostatic or fungistatic action could eventually be accepted to stabilize a preparation during the shelf-life of a unidose, nonsterile product. For the fungicidal and bactericidal preservative must be toxicologicaly acceptable.
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