It’s often said that our modern society is ‘too clean’, and as a result our immune systems aren’t up to scratch, compared to our ancestors’. However, not only is this not true, say researchers from UCL and the London School of Hygiene & Tropical Medicine, household cleanliness is still vital to stop the spread of infection.
Rates of childhood asthma and allergies have been on the rise since the Industrial Revolution. To explain this, in 1989, epidemiologist Prof David Strachan suggested that our hygiene was to blame: children weren’t contracting as many infections, meaning their immune systems weren’t being trained from an early age. As a result, they were developing allergic diseases such as hay fever.
Exposure to microbes is vital to developing a healthy immune system, the researchers say, but not infections – and certainly not all microbes. In a review of the evidence, the researchers found that the microbes we need are the ones we find in the natural environment, not the potentially infectious ones in the home.
“Exposure to microorganisms in early life is essential for the ‘education’ of the immune and metabolic systems,” said Graham Rook, Emeritus Professor of Medical Microbiology at UCL and lead author of the paper.
“Organisms that populate our guts, skin and airways also play an important role in maintaining our health right into old age: so throughout life we need exposure to these beneficial microorganisms, derived mostly from our mothers, other family members and the natural environment.
“But for more than 20 years there has been a public narrative that hand and domestic hygiene practices, that are essential for stopping exposure to disease-causing pathogens, are also blocking exposure to the beneficial organisms.”
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The researchers also suggest an alternative reason that allergic diseases may be on the rise. Though epidemiologists have found a link between household cleanliness and allergies, the cause isn’t the lack of microbes but the presence of cleaning fluids. These cleaners often include volatile organic compounds, or VOCs, which are a major component of air pollution in the home. When children breathe in VOCs, this can lead to damage in lung tissue, which in turn can lead to allergic diseases.
The team also stress that vaccines are an important component in children’s developing immune systems.
“So cleaning the home is good, and personal cleanliness is good, but, as explained in some detail in the paper, to prevent spread of infection it needs to be targeted to hands and surfaces most often involved in infection transmission,” Rook said. “By targeting our cleaning practices, we also limit direct exposure of children to cleaning agents.
“Exposure to our mothers, family members, the natural environment, and vaccines can provide all the microbial inputs that we need. These exposures are not in conflict with intelligently targeted hygiene or cleaning.”
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