Skin flora

The healthy skin is densely populated with microorganisms such as bacteria and fungi, which are a natural component of the skin surface as commensals or Mutualen and are summarized as skin flora. Make an important requirement is to protect the skin itself and the whole organism against pathogenic germs and are part of the microbiome.

If the skin is intact as the limiting organ to the outside world and its barrier function can meet only these germs do not bother, do not get sick and are very useful for several reasons. For as harmless may be for us the commensals, they are at the microscopic level aggressively endeavored to defend their turf. If a pathogen will penetrate into the body, so he must first of all with these " bouncers " mucking around. Only those claims against the resident flora, can penetrate deeper. Only secondarily produce metabolites which have a favorable effect on the properties of the skin.

The individual skin regions display a rather different spectrum of germs. The hair follicles thereby accommodate the majority of the germ, which is, among other things critical to the formation of so- common diseases such as acne or folliculitis.

  • 2.1 Seborrheic zones
  • 2.2 Moist skin areas
  • 2.3 Dry skin areas
  • 3.1 staphylococci
  • 3.2 corynebacteria
  • 3.3 propionibacteria
  • 3.4 Brevibacterium Dermabacter
  • 3.5 mushrooms
  • 3.6 micrococci
  • 3.7 more germs
  • 4.1 staphylococci: S. aureus
  • 4.2 Enterobacteriaceae
  • 4.3 Other bacteria: Aerobic Gram-positive spore-forming
  • 4.4 mushrooms, shed
  • 5.1 hair follicles as a seed reservoir
  • 5.2 Haarbalgmilbe


Moisture, pH and oxygen supply are very different depending on the area of ​​skin, and that describes the distribution of the individual "normal" bacteria are not strictly uniform. Depending on the skin region, age, gender, genetic predisposition and environmental conditions both the bacterial spectrum, as well as the counts of normal skin flora can be very different. Thus, a study of New York University, which examined the microbes on the forearms of six persons, a total of 182 different bacterial species from eight strains, but appeared only four species at all six people. The ratio of anaerobic to aerobic species is relatively balanced with 10:1. The nucleation densities, depending on the region 102-106 per cm ². Approximate counts of different skin regions ( number of bacteria per cm ²): fingertips 20-100, back 3 x 102 feet 102-103, forearm 102-5 x 103 hand 103, front 2 x 105, scalp, 106, Armpit 2 x 106 Total living around 1010 bacteria on our skin surface.

Horny layer

Aside from those microorganisms that have specialized in the degradation of keratin ( dermatophytes, Trichophyten ), the nutrient supply of the skin surface is limited and thus by far not all bacteria ideal. One of invasion is also the steady growth of the epidermis contrary, for the most populated cell layers (stratum disjunctum of the stratum corneum ) are continuously repelled.

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 longer was the oft-mentioned pH range of 5.4 to 5.9 than the normal value in the " forearm of a white, male, adult person " ( Braun-Falco / Korting 1986). Two recent studies have shown that the physiological pH is just below 5 ( Lambers et al 2006;. Segger et al, 2007. ). In addition, the pH of numerous factors is affected, such as age, gender, area of ​​skin, cosmetics etc.

The significance of the slightly acidic pH - value was also examined in numerous studies, and it could be shown that the growth of certain pathogenic microorganisms (e.g., Propionibacterium acnes ) inhibited by it, but the microorganisms of the normal flora (eg Staphylococcus epidermidis ) grow very well at a pH of around 5. Thus, the growth of non - pathogenic bacteria is the " acid mantle " stabilized and the pathogenic inhibited ( Pillsbury / Rebel 1952. Korting et al 1987, 1990 and 1992. Kurabayashi et al 2002;. Lambers et al 2006).

The importance of skin surface pH value is, however via the described addition, because by him work many pH -dependent enzymes very good, to the structure and the regeneration of the epidermal permeability barrier ( skin barrier ) are involved. Thus, the slightly acidic skin pH is of crucial importance to the overall homeostasis of the skin.


Despite the sweat glands and transdermal fluid secretion ( insensible perspiration ), the epidermis provides a very dry environment, which is a bad breeding ground. Difference was reflected in significantly higher seed densities in moist areas of the skin ( intertriginous ), such as the armpits, finger and toe webs, groin, anal fold.

Lipids, fatty acids

Free fatty acids, some of which are only formed by bacterial metabolism (lipophilic germs, see below), act on many types of bacteria bactericidal. A change in these milieu conditions also pulls shifts in the seed densities of the individual species and species by itself. For example, the proportion of lipophilic species in the state of Seborrhoeae and overall bacterial count increases with increased sweating (humidification otherwise dry skin ) to.

Skin regions with specific environment properties

Seborrheic zones

Talgreiche skin regions are particularly densely populated with lipophilic germs, these include: corynebacteria, propionibacteria and Malassezia furfur. The lipolytic metabolism of Propionibacterium acnes (including through lecithinases ) leads to the formation of free fatty acids, which in turn influence the rest of the population of the skin. In addition to these lipophilic germs (mainly Propionibacterium acnes ) also plenty of coagulase-negative staphylococci and non-pathogenic mycobacteria are present. Among the seborrheic areas include forehead, nasolabial folds, nose, neck and shoulders.

Moist skin areas

Increased moisture leads to an increase in the nucleation density. In the intertriginous areas (finger and toe webs, groin, armpits, anal fold ), the bacterial counts significantly higher than, for example, to the rather dry lower legs. The armpits are colonized very different, either outweigh coagulase-negative staphylococci next few corynebacteria or the opposite is the case. In the sweat transitions to Peptostreptococci settle, which are often the cause of an Schweißdrüsenabszesses. Spaces between the toes: pigment -forming Bacteroides species (B. melaninogenicus, B. asaccharolyticus ) and Clostridium perfringens are regularly detectable. Intertriginous areas are relatively frequently colonized with ( yeast ) fungus.

Dry skin areas

For example, flexor surface of the forearms: Overall low bacterial count. Coagulase negative staphylococci predominate ( 102-103 CFU / cm ²). Few corynebacteria and propionibacteria.

Resident flora


Staphylococci ( S. epidermidis, S. saprophyticus, S. hominis, S. xylosus, S. warneri, S. haemolyticus, S. saccharolyticus, S. Conii, p auricular ) preferably colonize moist and talgarme skin regions, such as intertriginous areas, hands and feet.


Corynebacteria (C. minutissimum, C. jeikeium, C. xerosis, C. pseudotuberculosis, C. goutcheri, C. pseudodiphteriticum, C. bovis ) cleave formed by the sebaceous glands of the skin fats to fatty acids for the acid environment on the skin are responsible and thus in turn lead to an inhibition of microbial growth.

Propionibacterium acnes

Propionibacterium ( P. acnes, P. granulosum, P. avidum ).

Brevibacterium Dermabacter

Creating including the individual's body odor.


While the skin of the feet has a variety of fungal flora, live on all other parts of the skin mainly species of the genus Malassezia.


Micrococci (M. luteus, M. flavus ) are detectable, especially in children.

More germs

Non-pathogenic mycobacteria, Sarcinia spp.

Transient bacterial colonization

Staphylococci: S. aureus



E. coli, Klebsiella, Pseudomonas and Enterobacteriaceae come on moist and warm skin regions ( intertriginous areas ) more frequently.

More germs: Aerobic Gram-positive spore-forming


Fungi, dandruff

The sebaceous glands of a human being too much sebum or sebaceous glands are clogged with these rare to wash your hair by sebum, then the normally harmless yeast Pitysporum allows oval strong growth, which leads to seborrheic eczema with itching and flaking. Shed be removed with suitable shampoos now get a good grip

Colonization of the hair follicle

Here are particularly high numbers predominantly lipophilic bacterial species. Near the surface settle Staphylococci and Malassezia, including aerobic corynebacteria and anaerobic at depth, lipophilic bacteria ( Propionibacterium ).

Hair follicles as a seed reservoir

A large part of the skin flora is located in the hair follicles, 20 % of the total flora of the skin is located in the deep portions of the hair follicles. These germs can not be eliminated by a skin disinfectant, they form the reservoir from which the skin flora after disinfection within 24 itself - is 72 hours again.


Demodex folliculorum as Haarbalgmilben live in the hair follicles of the scalp and on the scalp including forehead. Haarbalgmilben be passed from person to person, usually from mother to child, and colonize every human being, but also dogs and cats. The tiny mites eat grease, bacteria but also cream residues and makeup. After two weeks of life on the skin, they return to their place of birth, the hair follicle, where they mate and give birth. The new mite migrate to the hair growing back on the skin surface. Their existence helps maintain the balance on the skin. While they can cause mange in animals with weakened immune systems, negative effects in man and his partner Demodex folliculorum are not known.

Enumeration of bacteria on the skin ( detergent washing method )

A skin area of defined size is overlaid with a certain volume of detergent solution. The germs of the skin surface can be dissolved by vigorous rubbing in the detergent and grown after dilution.


  • Jörg Blech: Life on the people. Rowohlt, Reinbek 2000; revised edition ibid. 2010, ISBN 978-3-499-62494-0
  • Peter Brooke: Little monsters, the secret world of tiny creatures, Gondrom -Verlag, 1999, pp. 32/33