insufficiently repressed th1 and th2 responses, respectively. for example, all chronic inflammatory disorders show evidence of failed immunoregulation. secondly, helminths, non-pathogenic ambient pseudocommensal bacteria or certain gut commensals and probiotics, drive immunoregulation. they block or treat models of all chronic inflammatory conditions. evidence there is a significant amount of evidence supporting the idea that microbial exposure is linked to allergies or other conditions, although scientific disagreement still exists. since hygiene is difficult to define or measure directly, surrogate markers are used such as socioeconomic status, income, and diet. studies have shown that various immunological and autoimmune diseases are much less common in the developing world than the industrialized world and that immigrants to the industrialized world from the developing world increasingly develop immunological disorders in relation to the length of time since arrival in the industrialized world. this is true for asthma and other chronic inflammatory disorders. the increase in allergy rates is primarily attributed to diet and reduced microbiome diversity, although the mechanistic reasons are unclear. the use of antibiotics in the first year of life has been linked to asthma and other allergic diseases, and increased asthma rates are also associated with birth by caesarean section. however, at least one study suggests that personal hygienic practices may be unrelated to the incidence of asthma. antibiotic usage reduces the diversity of gut microbiota. although several studies have shown associations between antibiotic use and later development of asthma or allergy, other studies suggest that the effect is due to more frequent antibiotic use in asthmatic children. trends in vaccine use may also be relevant, but epidemiological studies provide no consistent support for a detrimental effect of vaccination/immunization on atopy rates. in support of the old friends hypothesis, the intestinal microbiome was found to differ between allergic and non-allergic estonian and swedish children (although this finding was not replicated in a larger cohort), and the biodiversity of the intestinal flora in patients with crohn's disease was diminished. limitations the hygiene hypothesis does not apply to all populations. for example, in the case of inflammatory bowel disease, it is primarily relevant when a person's level of affluence increases, either due to changes in society or by moving to a more affluent country, but not when affluence remains constant at a high level. the hygiene hypothesis has difficulty explaining why allergic diseases also occur in less affluent regions. additionally, exposure to some microbial species actually increases future susceptibility to disease instead, as in the case of infection with rhinovirus (the main source of the common cold) which increases the risk of asthma. treatment current research suggests that manipulating the intestinal microbiota may be able to treat or prevent allergies and other immune-related conditions. various approaches are under investigation. probiotics (drinks or foods) have never been shown to reintroduce microbes to the gut. as yet, therapeutically relevant microbes have not been specifically identified. however, probiotic bacteria have been found to reduce allergic symptoms in some studies. other approaches being researched include prebiotics, which promote the growth of gut flora, and synbiotics, the use of prebiotics and probiotics at the same time. should these therapies become accepted, public policy implications include providing green spaces in urban areas or even providing access to agricultural environments for children. helminthic therapy is the treatment of autoimmune diseases and immune disorders by means of deliberate infestation with a helminth larva or ova. helminthic therapy emerged from the search for reasons why the incidence of immunological disorders and autoimmune diseases correlates with the level of industrial development. the exact relationship between helminths and allergies is unclear, in part because studies tend to use different definitions and outcomes, and because of the wide variety among both helminth species and the populations they infect. the infections induce a type 2 immune response, which likely evolved in mammals as a result of such infections; chronic helminth infection has been linked with a reduced sensitivity in peripheral t cells, and several studies have found deworming to lead to an increase in allergic sensitivity. however, in some cases helminths and other parasites are a cause of developing allergies instead. in addition, such infections are not themselves a treatment as they are a major disease burden and in fact they are one of the most important neglected diseases. the development of drugs that mimic the effects without causing disease is in progress. public health the reduction of public confidence in hygiene has significant possible consequences for public health. hygiene is essential for protecting vulnerable populations such as the elderly from infections, preventing the spread of antibiotic resistance, and for combating emerging infectious diseases such as sars and ebola. the misunderstanding of the term "hygiene hypothesis" has resulted in unwarranted opposition to vaccination as well as other important public health measures.” it has been suggested that public awareness of the initial form of the hygiene hypothesis has led to an increased disregard for hygiene in the home. the effective communication of science to the public has been hindered by the presentation of the hygiene hypothesis and other health-related information in the media. cleanliness no evidence supports the idea that reducing modern practices of cleanliness and hygiene would have any impact on rates of chronic inflammatory and allergic disorders, but a significant amount of evidence that it would increase the risks of infectious diseases. the phrase "targeted hygiene" has been used in order to recognize the importance of hygiene in avoiding pathogens. if home and personal cleanliness contributes to reduced exposure to vital microbes, its role is likely to be small. the idea that homes can be made “sterile” through excessive cleanliness is implausible, and the evidence shows that after cleaning, microbes are quickly replaced by dust and air from outdoors, by shedding from the body and other living things, as well as from food. the key point may be that the microbial content of urban housing has altered, not because of home and personal hygiene habits, but because they are part of urban environments. diet and lifestyle changes also affects the gut, skin and respiratory microbiota. at the same time that concerns about allergies and other chronic inflammatory diseases have been increasing, so also have concerns about infectious disease. infectious diseases continue to exert a heavy health toll. preventing pandemics and reducing antibiotic resistance are global priorities, and hygiene is a cornerstone of containing these threats. infection risk management the international scientific forum on home hygiene has developed a risk management approach to reducing home infection risks. this approach uses microbiological and epidemiological evidence to identify the key routes of infection transmission in the home. these data indicate that the critical routes involve the hands, hand and food contact surfaces and cleaning utensils. clothing and household linens involve somewhat lower risks. surfaces that contact the body, such as baths and hand basins, can act as infection vehicles, as can surfaces associated with toilets. airborne transmission can be important for some pathogens. a key aspect of this approach is that it maximises protection against pathogens and infection, but is more relaxed about visible cleanliness in order to sustain normal exposure to other human, animal and environmental microbes.