horny layer
Apart from those microorganisms that have specialized in the degradation of the keratin (dermatophytes, trichophytic), the nutrient supply the skin surface limited and therefore far from ideal for all bacteria. An invasion is also reflected in the steady growth of the epidermis , for the most populated cell layers (stratum disjunctum of the stratum corneum) are shed continuously.
skin surface pH value
It has long been known that the skin surface is acidic (Heuss 1882), later they also spoke of the "acid mantle of the skin" ( Schade / Marchionini 1928). There have been numerous studies on the skin surface pH value and long the oft-mentioned pH range of 5.4 to 5.9 was regarded as the normal value on the "forearm of a white, male, adult person" (Braun-Falco / Korting 1986) . Two recent studies have shown that the physiological pH is just under 5 (Lambers et al. 2006; Segger et al. 2007). In addition, the pH value is influenced by many factors such as age, gender, area of skin, cosmetics, etc.
The importance of the slightly acidic pH was also investigated in numerous studies and It was shown that through him the growth of some pathogenic microorganisms (eg Propionibacterium acnes) but inhibited the normal flora of microorganisms to grow (eg Staphylococcus epidermidis) very well at a pH value by 5. Thus stabillisiert by the "acid mantle" the growth of non-pathogenic bacteria and the inhibition of pathogenic (Pillsbury / Rebel 1952; Korting et al. 1987, 1990 and 1992; Kurabayashi et al. 2002, Lambers et al. 2006).
The importance of the skin surface pH value goes beyond the described thing, because through him many pH-dependent enzymes work very well, which participated in the development and regeneration of the epidermal permeability barrier (skin barrier) are. Thus, the slightly acidic skin pH is of crucial importance for the whole of the skin homeostasis .
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