Mites, amoebae, flagellants and billions of microorganisms use humans as habitats, food sources and means of transport. The human ecosystem consists of about 1,000 arachnids, amoebae, fungi, a hundred billion bacteria and ten billion body cells. For every single human body cell, there are ten micro-organisms: We are a minority in our bodies.

Anyone who immediately thinks of pathogens forgets that microbiology fulfils vital functions. Adults‘ approx. 2 m² large skin surface is home to up to one million bacteria per cm², which protect the skin from external influences. The microbiological population of the mucous membranes in our digestive tract (approx. 400 m² surface area) is responsible for the division and uptake of food as well as for the stimulation of our immune system.
This multiplicity and variety of our „companions“ ensure that we are balanced, i.e. healthy. The microbiome – all the microorganisms of a living being – is the focus of current medical research.

Household living space
The own four walls in which the „human ecosystem“ lives offer an interesting habitat for other living things. Co-inhabitants who accompany us in our household until today started settling very quickly as far back as the first cave-people. Although houses have only been built for about 20,000 years – a very short period in terms of geological history – it quickly became necessary to adapt to these special, almost extreme habitats.
According to one estimate, the surface area of all flats worldwide is approximately 640,000 km². This corresponds approximately to the area of France. Only in recent years has science begun to take a closer look at the „household“ ecosystem and for the first time to investigate it more intensively. In a study, for example, 50 houses and households in the US state of North Carolina were examined for their insect colonisation. More than 10,000 insects from about 750 different species were collected in living areas, cellars and attics.
The household living space is characterised by extreme conditions, which are hardly found in nature: few to no plants, drought and low food resources. Vacuum cleaners, cleaning agents, but also pesticides increase the evolutionary pressure. Under these conditions, only very well adapted species such as pholcid spiders, house dust mites or silverfish can survive in the long term. Bedbugs, which in the middle of the last century were considered almost extinct due to the use of DDT and other insecticides in the industrial nations, became resistant within a few decades and are now on the rise again.

Microbiology at home
Above all, microorganisms also populate our homes. As part of the „Home Microbiome Project“ study, seven families and their households with 18 persons, three dogs and one cat were sampled daily over a period of three weeks, and approximately 22,000 species of microorganisms were detected. Microbiological „hotspots“ are not – as was often rumoured in the past – toilet seats, but door handles, light switches and above all mobile phones and PC keyboards. Moist cleaning cloths and sponges provide ideal conditions for microbiological growth.
Whoever tries to create sterile conditions with aggressive detergents or disinfectants starts a competition that cannot be won. Disinfection not only destroys pathogenic germs, but also the remaining microbiology. However, re-population occurs immediately and microorganisms adapt very quickly to conditions that are hostile to them, sometimes leading to the development of resistance. This phenomenon can be observed in hospitals, among other places and is referred to as infectious hospitalism.

Healthy microbiome
Findings from microbial research show that the diversity of the microorganisms in the human ecosystem and its household can be regarded as a source of health. At work, at home or partly in leisure activities: We spend up to 90 % of our lifetime in closed rooms, the microbiological settlement of which in turn influences us. A healthy microbiome in the household is, therefore, important for us and this is how we can boost it: Letting air in on a regular basis leads to a reduction of humidity in rooms and prevents the development of mould. It also allows a variety of good bacteria to enter buildings.