What’s your routine? Do you shower every morning, or skip a few days? Do you change the bedsheets weekly, or only when they get smelly? How about your towels: New ones – like clockwork – every Saturday, or do you wait until they are, well, just that a touch on the manky side?

We live in an age of cleanliness. Our soaps are antibacterial. Our household cleaners promise to kill 99.9% of germs. Microbes are bad, plain and simple.

But at the same time, some scientists also tell us that being too clean is also wrong, because it might help cause asthma and allergies. So is there a balance between keeping obsessively clean and learning to live with the bacteria all around us?

We have known since the late 19th Century – and the discoveries of German physician Robert Koch – that certain bacteria cause specific diseases. Since then, sanitation and cleanliness have dramatically improved our health.

Yet not all microbes are bad. Yes, there are bacteria that cause unpleasant or even deadly diseases, but lots of them are extremely useful and beneficial to our health. They make vitamins in our gut, coat our skin to protect us from harmful microbes, and help us digest food. Outside of our bodies, they decompose organic waste, make half the world's oxygen and fix nitrogen levels in the air – helping make the Earth the life-supporting planet it is. Today, many scientists argue that people have become “too clean” for their own good.

We need contact with the microbial biodiversity from the environment – Graham Rook, University College London

In 1989, the British epidemiologist David Strachan was the first to suggest that the exposure to infections during childhood would provide a good defence against allergies in later life. It’s an idea known as ‘Hygiene Hypothesis’.

An allergy is, in fact, our immune system going haywire, by perceiving a harmless substance as a major attack. Our bodies, says Dorothy Matthews, biologist at Russell Sage College in Troy, New York, may overreact to beneficial microbes, because our immune systems have forgotten how to live with them.

For this reason, we may have to understand how microbiota – the microorganisms living on and in our body – can help us. “It is essential to pass on the maternal microbiota – symbiotic harmless organisms in the gut, skin and elsewhere – and we need contact with the microbial biodiversity from the environment,” says Graham Rook, an epidemiologist at University College London.

Weeding out pathogens

Take a baby’s dummy that’s fallen to the floor. It’s better for the mother to suck it clean rather than provide a new sterile one, he says, because this has been shown to accelerate development of the infant's microbiota, and reduces allergies. One could arguably describe it as exposure therapy, starting with food. “Eat a varied diet, preferably with farm produce,” says Rook. It’s also better to exercise in nature, not a gym. And while we might think dogs are dirty, they also help most of us to increase microbial biodiversity and reduce allergies.

In a way, the immune system is like a farmer. It makes sure that our bodies have the microbes that are important for our development, physiology, metabolism, even brain functions, while at the same time doing plenty of weeding, getting rid of the microbes that contain pathogens. No wonder that a lack of diversity in our microbiota is associated with a huge range of illnesses. Having said that, there is still no convincing proof that the lack of a specific type of microbe can cause a particular disease. “This might well come one day,” says Rook, “but the problem is technically and statistically enormously complex.”

Others agree. “The microbiome has been linked to immunity, autism, allergy, autoimmunity, mood, and the development of our central nervous system,” says Mary Ruebush, microbiologist and instructor at Becker Professional Education School. And this exposure therapy begins the moment we are born – children who are delivered vaginally have much lower rates of allergy than those delivered via caesarean, possibly because of this early exposure to the mother’s normal vaginal flora, she adds.  

Our exposure to good microbes early in life can be an enormous benefit to our health, explains Rook. For instance, early exposure to microbes in our gut activates some immune cells in such a way that as we get older, they do not over-respond to microorganisms. Rook calls these microbes our “old friends”. And we are missing their friendship, because extreme cleanliness means that often we don’t come in contact with microbes in the same way that our ancestors did.

Overall obsessive washing ‘disrupts the normal flora which keep you healthy by competing with harmful organisms’

This presents something of a conundrum for people hoping to live healthier lives. How can we avoid disease from the bad bacteria, while still fostering the good bacteria? Rook certainly wouldn’t advocate skipping the essentials, such as washing your hands. Scientists consider dirty hands as one of the most likely reasons why infections are passed between us. Getting your hands clean is not just a question of how long you wash them, but how “well”. You have to apply soap and water, rub all surfaces of the hands thoroughly for at least 15 seconds, then rinse under running water and then dry them, say the experts. The rubbing with soap detaches the germs from your skin, while the rinsing takes them off the hands.

But not all of our body has to be washed so stringently. Overall obsessive washing “disrupts the normal flora which keep you healthy by competing with harmful organisms”, says Ruebush. “Operating your immune system in an environment of sterility is like a sensory deprivation for the brain. Eventually, it goes insane, thus the increased amount of allergy and autoimmunity associated with persons who try too hard to avoid all exposure to anything in their environment,” she says. A long shower every day may not be advisable, as it removes the “good bacteria” from our skin. But you should wash around your genitals and anywhere you sweat a lot. And you should change your underwear every day.

Around the house, the solution for fighting the wrong kind of bacteria is not excessive cleaning, but timely cleaning. Good hygiene is not a once-a-week, deep-down clean, it needs to be ”an ongoing part of our daily lives, where hygiene measures are targeted where and when necessary," says Sally Bloomfield, of the London School of Hygiene and Tropical Medicine, and chair of the International Scientific Forum on Home Hygiene.

Take chopping boards in the kitchen. If you cut your greens, it’s ok to wait until after dinner to do the washing up. Not so if you’ve chopped raw fish or meat. Instant action is required, or you could put your family at risk of infection.

After all, it’s well established that about 70% of all chicken are contaminated with Campylobacter, a bacterium which can cause food poisoning and will happily multiply on your chopping board.

Damp dangers

Hospital studies show bedlinen and towels can easily spread viruses and germs, but our homes are not quite the high-risk environment that will breed the next superbug. But fluffy wet towels can be a problem.

“There is no scientific data which could allow us to explicitly state how often we should change bed linen, towels etc,” says Bloomfield, but there is enough data to say that they can be an infection risk in the home. She recommends to change bedlinen and towels about once a week, and warns strongly against sharing hand towels and other personal care items.

Warm damp cloths are a particular haven for nasty bugs, says Bloomfield. That’s why cloths in both the kitchen and bathroom should ideally be discarded and washed after every use. Failing that, at least “rinse them well immediately after use and dry them,” recommends Bloomfield. Tea towels, meanwhile, are ideal for drying dishes, if you are keen to spread your germs to all the glasses and plates in your cupboard. Regular, even daily swaps are highly recommended. And laundry of towels and linen should be done at 60C (140F) to beat the bugs, or with “oxygen-based bleaching agents” in the washing powder if it’s done at lower temperatures.

When it comes to bathrooms, it doesn’t help, of course, that all-too-few people close the toilet lid when flushing. If you can’t be bothered, remember that an open lid is a gateway for all the bacteria inside to spread and multiply.

Let your children play in places where they have contact with soil and vegetation, which are rich in beneficial microbes – Ilkka Hanski

Pyjamas are another weak point in many people’s personal hygiene. Some surveys suggest that many make the smell test before putting them in the wash. Change them at least once a week, say the experts. Ultimately, it’s all about getting on top of the “critical [infection] control points,” says Bloomfield.

The overall message, then, is not that we should return to living in squalor as to try to embrace good bacteria; we need to be just as vigilant without our homes to keep them free from germs. Instead, Ilkka Hanski, a biologist at the University of Helsinki in Finland, says, it’s important to get out of the house and spend time in woodlands and forests. “Let your children play in places where they have contact with soil and vegetation, which are rich in beneficial microbes,” he says. “If you have a house, don’t maintain a lawn, let native plants take over and grow taller. Cut them once or twice a year.”

Strength after sickness

Studies show the benefits. Children who grew up in an environment that was not obsessively clean have lower rates of allergy and asthma. And certain bacteria also actively protect us from bowel disease and even some types of anxiety and depression.

A healthier life, it seems, can be boosted by exposure to farm animals and harmless but vital microorganisms in dirt, food, and water. “Microbial exposure is important for promoting the development of effective regulatory pathways that keep inflammation under control,” says Thom McDade, a biological anthropologist Northwestern University in Evanston, Illinois.

If the “hygiene hypothesis” is correct, it may explain the rapid rise of both asthma and allergy cases during the past 20 years. Of course, there are other explanations too, for example public health trends such as the widespread use of purified water, the overuse of antibiotics, and – of course – changes in our environment such as higher levels of pollution.

“It is likely that many factors that are part of the Western lifestyle are involved. Antibiotics will disturb the beneficial microbes in our bodies and thereby harm the immune responses,” says Hanski. In contrast, he adds, studies clearly show that vaccines are not harmful and play no role in the increase in allergies.

On the plus side, says Ruebush, you can take heart in knowing that every time you get a little sick, you get a little stronger. “The message is not one that most people want to hear: they want the quick pharmaceutical fix for the slightest bit of discomfort. But every time you take the quick fix, you make your body a little weaker.” That’s something to remember the next time you’re tempted to slather on the shower gel.

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