At first sight, hygiene in our modern world seems to be rather satisfactory. Nevertheless, vulnerable groups are increasing in our society, which means that hygiene is a crucial factor in the well-being of the many people involved. Moreover, in the Netherlands, for instance, there are an estimated 2 million food-borne infections every year, of which 30 to 50% is supposed to find its origin in family homes. This indicates that important factors in daily life such as food preservation and preparation generally are far from hygienic. This is probably due to contaminated foodstuffs on one hand, and on the other a serious lack of knowledge in the population about food handling and preservation, as well as about cleaning and disinfection procedures. Inadequate knowledge can also lead to hygiene problems when dealing with modern technical facilities in the home like humidifiers, refrigerators and microwave ovens, airconditioning systems and hot water supplies. Micro-organisms are very flexible and can adapt themselves very rapidly to any new situation that is created by man. Excessive insulation of homes may lead to increased internal humidity the occurrence of house dust mites and moulds, and, as a consequence, increased incidence of allergy symptoms. All new and old hazards should be death with, for instance by education of the general population, proper hygiene design, as well as adequate cleaning techniques in order to reach and maintain the hygiene level that is generally required.