The survival and reproduction of microbes in cosmetics is dependent on some environmental factors: physical temperature, environmental pH, osmotic pressure, radiation, static pressure, and chemical sources, nutrients (C, N, P, S source), oxygen, organic growth factors. Based on this, the mechanism of preservatives can be summarized briefly.
1) in some products with low moisture content such as ointments, microbes are usually difficult to grow under normal conditions.
2) for most bacteria, the most suitable PH range is close to neutral (6.5~7.5), strong acid and strong alkali are not suitable for the growth of microbes, such as the common fruit acid products, the anticorrosion effect is usually parallel to the neutral product;
3) increasing or decreasing osmotic pressure can lead to rupture of cell membrane and contraction and dehydration of membrane.
4) the other surface tension is also one of the factors that affect the growth of microbes. In some formulations with high dosage of surfactants, microbes are not easy to grow. In this respect, the cationic surfactants are more prominent, and the physiological toxicity of anions and non ions to microbes is very small.
5) in general, the most suitable temperature for producing bacteria is 30 ~37 C, and the mold and yeast are 20 C ~25 C, so the method of high temperature disinfection can be adopted, but individual bacillus can produce protective film after adapting to the environment, even if the temperature of 80 C ~90 C is not killed at high temperature in a short time.
The effect of preservatives on microorganisms is only possible if they are directly exposed to microorganisms. Preservative is the first contact with the outer membrane, adsorption, through the cell membrane into the cytoplasm, and then can play the efficacy in various parts to prevent cell reproduction or kill it. In fact, it is mainly the effect of antiseptic on cell wall and cell membrane, in addition to the activity of enzymes that affect the metabolism of cells, or the influence on the structure of a part of the cytoplasm.
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