“The Hygiene Hypothesis” Are we too clean for our own good?

the hygiene hypothesis
the hygiene hypothesis

Are we too clean for our own good?

Many people think our obsession with cleanliness is to blame for the rise in allergies such as hay fever, eczema and asthma.

The idea is that modern hygiene standards have reduced our exposure to good and bad germs, which can help strengthen the immune system, the body’s mechanism for keeping us healthy.

Over the past 20 years there has been a rise in allergies, and no-one really knows why. Around one in four people in the UK suffers from an allergy at some point in their lifetime and numbers are increasing every year.

Research suggests that exposure to germs is only one possible reason for this and diet, lack of exercise, our environment, use of antibiotics and a family history of allergies may play a bigger role.

But what is increasingly clear from the evidence is that hygiene standards should not be relaxed to try to reduce the risk of developing an allergy.

Are we being too clean?

No. It is very important that we maintain good standards of personal and home hygiene.

Good hygiene is about avoiding infection and preventing the spread of infection to others. Good hygiene isn’t about being dirt-free and doesn’t require being obsessively clean. Good hygiene is about preventing the spread of germs at times and in places and situations where it really matters, such as when preparing food, after using the toilet, after sneezing and when someone’s ill with an infection.

Find out how to prevent germs from spreading.


Where did this idea of being ‘too clean’ originate?

The idea is based on “the hygiene hypothesis”, first proposed in a 1989 study by Prof David Strachan, which suggests that a lack of childhood exposure to harmful germs and fewer childhood infections are to blame for the rise in allergies.

Although it is catchy, the phrase “hygiene hypothesis” is somewhat misleading and it has been wrongly used in the media to suggest that modern hygiene standards are bad for our health.

It is important that we do not relax our personal and home hygiene standards. Exposure to germs is only one of several reasons that could explain the rise in allergies and may not be the most important one.

Check an interactive guide on hygiene hypothesis from the International Scientific Forum on Home Hygiene.

Can homes really be ‘too clean’?

No amount of cleaning can rid the home of germs. As fast as they are removed by cleaning, new germs return via humans and pets, contaminated food, the outside air etc. The idea that we now live in sterile homes is totally wrong. It’s impossible to sterilise our homes.


Why is hygiene important?

Good hygiene is critical in stopping the spread of disease-causing germs, such as colds and flu, tummy bugs like campylobacter, salmonella and E. coli O157, in the home and beyond, on food, from our pets and between people. Particular care should be taken to protect at-risk groups such as babies, whose immune systems have not fully developed, and people with a weakened immune system because of illness or medication.


Doesn’t exposure to germs strengthen our immune system?

It is thought that exposure to both good and bad germs in the first few years of life helps to develop the immune system – an idea distinct to the hygiene hypothesis. This helps the body to learn how to fight infection and to tell the difference between harmful and harmless substances.

Throughout life, it is also important that our bodies have the right balance of some exposure to both good and bad germs (present in our everyday environment), particularly in our gut and on our skin, to ensure that the immune system is trained to deal with different kinds of substances. Changes in this balance can cause the immune system to react unpredictably and it may find it difficult to tell when it is being attacked.

Maintaining this balance means not being afraid of getting outside and getting dirty sometimes. However, you should take every precaution to reduce your exposure to harmful germs by ensuring good personal and home hygiene, particularly if you are in an at-risk group.

Exposure to germs such as E.coli, norovirus and the measles virus can be very dangerous and can lead to life-threatening illnesses. These types of infection can cause permanent damage to your body and immune system so it cannot fight infection as well when it is attacked again.

People who maintain a healthy lifestyle tend to have a stronger immune system. Lifestyle factors that can weaken the immune system include drinking too much alcohol, poor diet and stress.

But can’t you develop immunity to germs like salmonella, E. coli, flu and so on?

To a certain extent, yes. Coming into contact with a specific harmful germ such as salmonella or measles will cause the body to respond and make antibodies, which neutralise the germ and protect against that particular germ. But deliberately exposing yourself to such germs is risky because you may become very seriously ill before your body can respond and fight the infection – and if you survive you will only have developed immunity against that particular germ.

This is why we developed vaccines so that we can be exposed to small safe doses of germs such as the flu, the measles virus and so on in a carefully controlled way that gives us protection without making us ill.


So what else could explain the rise in allergies?

Allergies have risen sharply over the past two decades and we’re not entirely sure why. Changes to the types of germs we come into contact with is only one factor among many that may explain this rise. Other factors include changes in diet and eating allergy-causing foods, where we live, a family history of allergy and how physically active we are.

One theory suggests that we have lost touch with a bunch of good germs, known as “old friends”, that humans evolved alongside back in the Stone Age, when our immune system was still developing. How this may have come about isn’t entirely clear, but measures to protect us from harmful germs – such as public sanitation – may have inadvertently cut us off from these good germs, which live in similar environments.


Who are these old friends?

Scientists aren’t entirely sure, but research suggests they include some of the good germs found on the skin, gut and throat area as well as in our outdoor environment, especially the countryside, which may explain why children on farms have less asthma. These old friends are not thought to include harmful germs that spread infectious diseases such as colds, flu, measles, salmonellosis, norovirus etc.

For more information on the old friends theory, read  The Hygiene Hypothesis and its implications for home hygiene, lifestyle and public health (International Scientific Forum on Home Hygiene).


Should we therefore be more relaxed about hygiene?

Even good old countryside dirt can contain harmful germs. So, relaxing hygiene would only expose us to “new enemies”, like E. coli O104, not our old friends. That would raise the risk of infectious disease and take us back to the days when lives were short and one in four children died before the age of five.


So are you less likely to develop allergies if you live on a farm?

There is some evidence that children who grow up on farms develop fewer allergies. The theory is that farms (particularly farm animals) increase exposure to different types of good and bad germs, which stimulate the immune system and reduce the risk that someone will develop an allergy.

Are the chemicals in cleaning products linked to the rise in allergies?

No, there is currently no evidence that links the use of household cleaning products, or their ingredients, such as antibacterial agents, to the rise in allergies, such as hay fever and asthma.


Is personal hygiene a likely factor in the rise in allergies?

Bathing and showering does remove germs from our skin but there is no evidence linking frequency of washing, showering or bathing to an increased risk of allergies.


Are antibiotics to blame for the rise in allergies?

There is some evidence linking the use of antibiotics with the rise in allergies. It is thought that antibiotics may reduce the amount of germs on our skin and in our gut. This upsets the body’s normal balance and the immune system finds it difficult to tell the difference between harmless and harmful germs.


Are vaccines to blame for the rise in allergies?

Vaccines are not thought to be associated with rising allergy levels. Vaccination has saved more lives and prevented more serious diseases than any advance in recent medical history.

Vaccines work by stimulating our immune system to produce antibodies (substances produced by the body to fight disease) without actually infecting us with the disease. As with all new medicines, all vaccines are extensively tested for safety before they’re made routinely available to the general public. Find out more about vaccinations.


Are changes in diet to blame for the rise in allergies?

There is some evidence that changes to childhood diets may be responsible for an increase in allergies.

It is thought that introducing foods that can cause an allergy (allergens) such as peanuts, milk and egg during weaning and alongside continued breastfeeding, can reduce the number of children developing allergic disease in later childhood. However, this is only a theory and there are currently a number of studies ongoing around the world that aim to answer this very important question.

Until we know the answer, mothers should continue to follow the current national advice, which is to exclusively breastfeed your baby for around the first six months of their life and not to give them allergenic foods before six months of age, such as peanuts, nuts, seeds, egg, fish, shellfish, milk, soya, wheat (and other cereals that contain gluten such as rye, barley and oats). Find out more about breastfeeding and weaning.

Allergic rhinitis – how to prevent allergic rhinitis?

Allergic rhinitis - a guide
Allergic rhinitis – a guide

The best way to prevent allergic rhinitis is to avoid the allergen that causes it.

But this isn’t always easy. Allergens, such as dust mites, aren’t always easy to spot and can breed in even the cleanest house.

It can also be difficult to avoid coming into contact with pets, particularly if they belong to friends and family.

Below is some advice to help you avoid the most common allergens.

House dust mites

Dust mites are one of the biggest causes of allergies. They’re microscopic insects that breed in household dust.

To help limit the number of mites in your house, you should:

consider buying an air-permeable occlusive mattress and bedding covers – this type of bedding acts as a barrier to dust mites and their droppings

choose wood or hard vinyl floor coverings instead of carpet

fit roller blinds that can be easily wiped clean

regularly clean cushions, soft toys, curtains and upholstered furniture, either by washing or vacuuming them

use synthetic pillows and acrylic duvets instead of woollen blankets or feather bedding

use a vacuum cleaner fitted with a high efficiency particulate air (HEPA) filter – it can remove more dust than ordinary vacuum cleaners

use a clean damp cloth to wipe surfaces – dry dusting can spread allergens further

Concentrate your efforts on controlling dust mites in the areas of your home where you spend most time, such as the bedroom and living room.


It isn’t pet fur that causes an allergic reaction, but exposure to flakes of their dead skin, saliva and dried urine.

If you can’t permanently remove a pet from the house, you may find the following tips useful:

keep pets outside as much as possible or limit them to one room, preferably one without carpet

don’t allow pets in bedrooms

wash pets at least once a fortnight

groom dogs regularly outside

regularly wash bedding and soft furnishings your pet has been on

If you’re visiting a friend or relative with a pet, ask them not to dust or vacuum on the day you’re visiting because it will disturb allergens into the air.



Different plants and trees pollinate at different times of the year, so when you get allergic rhinitis will depend on what sort of pollen(s) you’re allergic to.

Most people are affected during the spring and summer months because this is when most trees and plants pollinate.

To avoid exposure to pollen, you may find the following tips useful:

check weather reports for the pollen count and stay indoors when it’s high

avoid line-drying clothes and bedding when the pollen count is high

wear wraparound sunglasses to protect your eyes from pollen

keep doors and windows shut during mid-morning and early evening, when there’s most pollen in the air

shower, wash your hair and change your clothes after being outside

avoid grassy areas, such as parks and fields, when possible

if you have a lawn, consider asking someone else to cut the grass for you

Mould spores

Moulds can grow on any decaying matter, both in and outside the house. The moulds themselves aren’t allergens, but the spores they release are.

Spores are released when there’s a sudden rise in temperature in a moist environment, such as when central heating is turned on in a damp house or wet clothes are dried next to a fireplace.

To help prevent mould spores, you should:

keep your home dry and well ventilated

when showering or cooking, open windows but keep internal doors closed to prevent damp air spreading through the house, and use extractor fans

avoid drying clothes indoors, storing clothes in damp cupboards and packing clothes too tightly in wardrobes

deal with any damp and condensation in your home

Read more about how damp and mould can affect your health and how to get rid of damp and mould.

Allergic rhinitis – What are the signs and symptoms of Allergic rhinitis? Part One

Allergic rhinitis - a guide
Allergic rhinitis – a guide

Allergic rhinitis is inflammation of the inside of the nose caused by an allergen, such as pollen, dust, mould, or flakes of skin from certain animals.

It’s a very common condition, estimated to affect around one in every five people in the UK.

Signs and symptoms

Allergic rhinitis typically causes cold-like symptoms, such as sneezing, itchiness and a blocked or runny nose. These symptoms usually start soon after being exposed to an allergen.

Some people only get allergic rhinitis for a few months at a time because they’re sensitive to seasonal allergens, such as tree or grass pollen. Other people get allergic rhinitis all year round.

Most people with allergic rhinitis have mild symptoms that can be easily and effectively treated. But for some symptoms can be severe and persistent, causing sleep problems and interfering with everyday life.

The symptoms of allergic rhinitis occasionally improve with time, but this can take many years and it’s unlikely that the condition will disappear completely.

When to see your GP

Visit your GP if the symptoms of allergic rhinitis are disrupting your sleep, preventing you carrying out everyday activities, or adversely affecting your performance at work or school.

A diagnosis of allergic rhinitis will usually be based on your symptoms and any possible triggers you may have noticed. If the cause of your condition is uncertain, you may be referred for allergy testing.

Read more about diagnosing allergic rhinitis.

What causes allergic rhinitis?

Allergic rhinitis is caused by the immune system reacting to an allergen as if it were harmful.

This results in cells releasing a number of chemicals that cause the inside layer of your nose (the mucous membrane) to become swollen and excessive levels of mucus to be produced.

Common allergens that cause allergic rhinitis include pollen – this type of allergic rhinitis is known as hay fever – as well as mould spores, house dust mites, and flakes of skin or droplets of urine or saliva from certain animals.

Read more about the causes of allergic rhinitis.

Treating and preventing allergic rhinitis

It’s difficult to completely avoid potential allergens, but you can take steps to reduce exposure to a particular allergen you know or suspect is triggering your allergic rhinitis. This will help improve your symptoms.

If your condition is mild, you can also help reduce the symptoms by taking over-the-counter medications, such as non-sedating antihistamines, and by regularly rinsing your nasal passages with a salt water solution to keep your nose free of irritants.

See your GP for advice if you’ve tried taking these steps and they haven’t helped. They may prescribe a stronger medication, such as a nasal spray containing corticosteroids.

Read more about treating allergic rhinitis and preventing allergic rhinitis.

Further problems

Allergic rhinitis can lead to complications in some cases. These include:

nasal polyps – abnormal but non-cancerous (benign) sacs of fluid that grow inside the nasal passages and sinuses

sinusitis – an infection caused by nasal inflammation and swelling that prevents mucus draining from the sinuses

middle ear infections – infection of part of the ear located directly behind the eardrum

These problems can often be treated with medication, although surgery is sometimes needed in severe or long-term cases.

Allergic rhinitis – what are the cause of Allergic rhinitis? Part 2

Allergic rhinitis - a guide
Allergic rhinitis – a guide

Allergic rhinitis is caused by an allergic reaction to an allergen, such as pollen, dust and certain animals.

Oversensitive immune system

If you have allergic rhinitis, your immune system – your natural defence against infection and illness – will react to an allergen as if it were harmful.

If your immune system is oversensitive, it will react to allergens by producing antibodies to fight them off. Antibodies are special proteins in the blood that are usually produced to fight viruses and infections.

Allergic reactions don’t occur the first time you come into contact with an allergen. The immune system has to recognise and “memorise” it before producing antibodies to fight it. This process is known as sensitisation.

After you develop sensitivity to an allergen, it will be detected by antibodies called immunoglobulin E (IgE) whenever it comes into contact with the inside of your nose and throat.

These antibodies cause cells to release a number of chemicals, including histamine, which can cause the inside layer of your nose (the mucous membrane) to become inflamed and produce excess mucus. This is what causes the typical symptoms of sneezing and a blocked or runny nose.

Common allergens

Allergic rhinitis is triggered by breathing in tiny particles of allergens. The most common airborne allergens that cause rhinitis are described below.

House dust mites

House dust mites are tiny insects that feed on the dead flakes of human skin. They can be found in mattresses, carpets, soft furniture, pillows and beds.

Rhinitis isn’t caused by the dust mites themselves, but by a chemical found in their excrement. Dust mites are present all year round, although their numbers tend to peak during the winter.

Pollen and spores

Tiny particles of pollen produced by trees and grasses can sometimes cause allergic rhinitis. Most trees pollinate from early to mid-spring, whereas grasses pollinate at the end of spring and beginning of summer.

Rhinitis can also be caused by spores produced by mould and fungi.


Many people are allergic to animals, such as cats and dogs. The allergic reaction isn’t caused by animal fur, but flakes of dead animal skin and their urine and saliva.

Dogs and cats are the most common culprits, although some people are affected by horses, cattle, rabbits and rodents, such as guinea pigs and hamsters.

However, being around dogs from an early age can help protect against allergies, and there’s some evidence to suggest that this might also be the case with cats.

Work-related allergens

Some people are affected by allergens found in their work environment, such as wood dust, flour dust or latex.

Who’s most at risk?

It isn’t fully understood why some people become oversensitive to allergens, although you’re more likely to develop an allergy if there’s a history of allergies in your family.

If this is the case, you’re said to be “atopic”, or to have “atopy”. People who are atopic have a genetic tendency to develop allergic conditions. Their increased immune response to allergens results in increased production of IgE antibodies.

Environmental factors may also play a part. Studies have shown certain things may increase the chance of a child developing allergies, such as growing up in a house where people smoke and being exposed to dust mites at a young age.

How to recognise Hay Fever

For more information on hay fever and other allergies please check out our previous blogs.


Infographic via Infographic.ca