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Your surrounds may be safer but your immune system has never been weaker

Leading physicians and immunologists are beginning to re-evaluate the antiseptic, at times even hysterical, ways in which we interact with our environment.

New York

SHOULD you use anti-bacterial soap or hand sanitisers? No. Are we taking too many antibiotics? Yes.

"I tell people, when they drop food on the floor, please pick it up and eat it," said Dr Meg Lemon, a dermatologist in Denver who treats people with allergies and autoimmune disorders. "Get rid of the anti-bacterial soap. Immunise! If a new vaccine comes out, run and get it. I immunised the living hell out of my children."

She posits that our immune system can become disrupted if it doesn't have regular interactions with the natural world.

"Our immune system needs a job," Dr Lemon said. "We evolved over millions of years to have our immune systems under constant assault. Now they don't have anything to do." She isn't alone. Leading physicians and immunologists are reconsidering the antiseptic, at times hysterical, ways in which we interact with our environment.

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Why? Let us turn to 19th-century London. The British Journal of Homeopathy Volume 29, published in 1872, included a startlingly prescient observation: "Hay fever is said to be an aristocratic disease. And there can be no doubt that, if it is not almost wholly confined to the upper classes of society, it is rarely, if ever, met with but among the educated." Hay fever is a catch-all term for seasonal allergies to pollen and other airborne irritants.

With this idea that hay fever was an aristocratic disease, British scientists were on to something. More than a century later, in November 1989, another highly influential paper was published on the subject of hay fever. The paper was short, less than two pages, titled Hay Fever, Hygiene, and Household Size. The author looked at the prevalence of hay fever among 17,414 children born in March 1958. Of 16 variables the scientist explored, he described as "most striking" an association between the likelihood that a child would get hay fever allergy and the number of his or her siblings.

It was an inverse relationship, meaning the more siblings the child had, the less likely it was that he or she would get the allergy. Not just that, but the children least likely to get allergies were ones who had older siblings.

The paper hypothesised that allergic diseases were prevented by infection in early childhood, transmitted by unhygienic contact with older siblings, or acquired prenatally from a mother infected by contact with her older children.

'Hygiene hypothesis'

"Over the past century declining family size, improvements in household amenities, and higher standards of personal cleanliness have reduced the opportunity for cross infection in young families," the paper continued. "This may have resulted in more widespread clinical expression of atopic disease, emerging in wealthier people, as seems to have occurred for hay fever."

This is the birth of the "hygiene hypothesis". The ideas behind it have since evolved and expanded, but it provides profound insight into a challenge that human beings face in our relationship with the modern world.

Our ancestors evolved over millions of years to survive in their environments. For most of human existence, that environment was characterised by extreme challenges, such as scarcity of food, or food that could carry disease, as well as unsanitary conditions and unclean water, withering weather, and so on. It was a dangerous environment, a heck of a thing to survive.

At the centre of our defences was our immune system, our most elegant defence. The system is the product of centuries of evolution, as a river stone is shaped by water rushing over it and the tumbles it experiences on its journey downstream.

A scientist who led efforts at the World Health Organization to develop global policy to limit use of antibiotics said that, philosophically, this is a lesson that runs counter to a century of marketing: We're not safer when we try to eliminate every risk from our environment.

"We have to get away from the idea of annihilating these things in our local environment," said Dr Keiji Fukuda. "It just plays upon a certain fear." Has much of our hygiene been practical, valuable, life-preserving? Yes.

Have we overcorrected? At times. Is that urge to pick your nose part of a primitive strategy to inform your immune system about the range of microbes in your environment and train your most elegant defence?

Yes. Perhaps. In short, from a cultural standpoint, you still probably shouldn't pick in public. But from a scientific standpoint, it is a surprisingly fair question. NYTIMES

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