What is the evidence for a causal link between hygiene and infections?

Even in an era in which access to personal "cleanliness" and a public health infrastructure are readily available in developed countries, illnesses associated with day care centres and homes continue to be a problem. The inhabitants of less developed countries, on the other hand, must contend with an inadequate public health infrastructure, lack of education programmes, and economic limitations in obtaining hygiene products. Therefore, less developed countries carry a greater burden of morbidity and mortality from infectious illnesses. The objective of this review is to examine and assess the epidemiological evidence for a causal relation between hygiene practices and infections. The Medline database was searched from January 1980 to June 2001 and studies were included if the outcome(s) was infection or symptoms of infection, and if the independent variable(s) was one or more hygiene measures. The strength of the association as measured by the relative reduction in risk of illness was appreciable and generally greater than 20%. Despite methodological strengths and limitations of the studies assessed, the weight of evidence collectively suggests that personal and environmental hygiene reduces the spread of infection. The results from this review demonstrate that there is a continued, measurable, positive effect of personal and community hygiene on infections.