According to a recent study from UCL and London School of Hygiene & Tropical Medicine, the theory that modern society is too clean leads to children's defective immune systems should not be believed.
The 'hygiene hypothesis,' in medicine, states that childhood exposure to certain microorganisms helps to prevent allergic diseases and contributes to the development the immune system.
There is however a common view that Western 21st Century society is too clean. This means that children and toddlers are less likely to become allergic to germs.
Researchers point out four reasons in this paper published in Journal of Allergy and Clinical Immunology. They conclude that we are not too clean for our own good.
Graham Rook, Emeritus Professor in Medical Microbiology at UCL Infection & Immunity, was the lead author. He stated: "Exposure early in life to microorganisms is essential for the education' of the immune system and metabolic systems.
"Organisms in our guts, skin, and airways play an important role for maintaining our health into old age. We need to be exposed to beneficial microorganisms throughout our lives, mostly from our mothers and other family members.
"But, for over 20 years, there has been a public narrative suggesting that household hygiene practices, which are crucial for preventing exposure to disease-causing pathogens such as HIV, also block exposure to beneficial organisms.
"This paper attempts to resolve the conflict between hygiene and cleaning to prevent infection and the need to provide microbial inputs for our digestive and immune systems.
Researchers identified four factors in a review of the evidence.
First, microorganisms that are found in modern homes are not necessarily the ones we need to be immune.
Second, vaccines are not only effective in protecting us against the infection they target but also strengthen our immune system so that we no longer have to be at risk of getting sick from pathogens.
Third, we now know that microorganisms in the natural green environment are especially important for our health. Domestic cleaning and hygiene do not affect our exposure to the environment.
Recent research has shown that if epidemiologists discover an association between cleaning the house and allergies, it is not usually due to the removal of organisms but rather because the lungs are exposed to cleaning products that cause damage that encourages the development allergic reactions.
Professor Rook said: "So cleaning your home and personal hygiene is great, but to prevent the spread of infection, it is important to focus on the surfaces and hands that are most likely to transmit infection. We can reduce the direct exposure of children and their parents to cleaning agents by focusing on our cleaning habits.
"Exposure to our mothers and family members, as well as the natural environment and vaccines, can provide all the necessary microbial inputs. These exposures can be combined with targeted hygiene and cleaning.