Environmental Allergies

Something in the air?

Environmental triggers can include both airborne particles, such as dust, pollen and mold spores, or chemical pollution, though the two problems are often inextricably bound together. Be sure to read the section which explains what you need to do about chemical overload and detox.

When to suspect environmental allergies and hypersensitivity

Suspect environmental allergies if your symptoms change as you re-locate in different places or at different times. If you are well at home but feel bad at work, an environmental allergen or chemical pollutant in your work environment may be to blame. Perhaps you are better on holiday (away from home); that would suggest an environmental factor, but be careful – you may eat differently on vacation, where normal habits do not apply!

Classic summer symptoms are a sign of a reaction to airborne allergens, such as pollen and mold. But some individuals are worse in winter. On hearing this I immediately suspect indoor pollution; in winter time we close our doors and windows, turn up the furnace and suffer from combustion fumes. Indoor chemical pollution can rise to many times the levels that would be permitted by safety regulations at work! Lack of fresh air also raises humidity which allows house dust mite and molds to flourish.


It looks like an allergy but food testing failed to solve it
You are worse in certain locations
You are worse at certain times of the day or year
Your symptoms are centered on the respiratory system (nose, larynx, trachea and lungs
REMEMBER: food allergies can also cause coughing, wheezing, sneezing and catarrh. Don’t be fooled!

What do we mean by environmental allergies?

Environmental or inhalant (breathed in) allergies are quite common. Indeed, for half a century they were the only kind to be recognized. Allergens can include such diverse substances as pollens, dust-mite (an almost invisible small animal), feathers, mold, fur and fabrics. The one thing these substances all have in common is that they are light enough to float in air and so be breathed in. Thus the target area is often the nasal and respiratory passages. However I discovered early on, by challenging sensitive individuals, that even a dust or mold allergy can induce strong and unwelcome mental reactions, such as altered perception or inappropriate changes of mood.

[Special note: There is an interesting overlap here. Sometimes a food allergic individual may react to “food dust”, that is, small particles of food, such as flours and meal, inhaled during cooking or baking. This can be bad news for a chef. One patient was convinced she was allergic to her horse but I discovered, happily for her, that she was reacting only to the grain meal which usually puffed into her face when mixing his feed!]

We can classify inhalant allergies of this type into two main categories:

  1. Seasonal and
  2. Non-seasonal (sometimes known as perennial)

Seasonal triggers are due to pollens and mold spores. 20% of the US population is affected by seasonal allergies, that is, up 35 million sufferers. Non-seasonal triggers include dust, mold and chemicals.

Nowadays, thanks to the pioneer work of my great mentor Theron Randolph, we recognize the widespread and diverse manifestations of chemical sensitivity. You will sometimes hear the expression “chemical allergy” but this attracts criticism. I have introduced a better concept: low-grade poisoning. The fact is that almost all chemicals are toxic and when inhaled over long periods, even in small quantities, can produce cumulative overload and symptoms. But some individuals are more susceptible than others, and react at levels most of us can tolerate. Some unlucky patients are exquisitely sensitive and react adversely to even the smallest traces of certain substances. We can label them chemically hypersensitive. Often there are complex reactions intermixed and the term multiple chemical sensitivity has come into common use.

Such susceptibility produces reactions which are easily confused with true inhalant allergens. Sometimes, of course, the two coexist within the same individual. Always bear in mind the possibility of chemical sensitivity when investigating symptoms due to apparently airborne triggers.


Dust and dust-mite

We put these two together for practical purposes. These are probably the most widely known, and suffered, inhalant allergies. Individuals sensitive to one, usually also react badly to the other (but not necessarily).

House dust is a mixture of particles of food, human skin scales, hair and grits but the main ingredient is fabric fibres or flock, worn away from carpets, clothes, upholstery and drapes. House dust mite is a living organism and seen under a microscope, looking grotesque and alarming, it seems to well deserve its fearsome scientific name, Dermatophagoides. There are two main strains, D. farinae prevalent in the United States, and D. pterynisinus more usual elsewhere. Actually the allergy is to the creature’s excrement rather than its body parts. Dust mite is found mainly in mattresses and pillows, but also bedroom carpets, bathroom carpets, lounge carpets, loafing chairs and settees – in fact, anywhere that human skin scales fall, since that is what it feeds on (Dermatophagoides means literally skin eater). Sometimes the infestation may be so severe that it is seen as a grey fine dust settling on polished furniture; very different from the fluffy dust which is the usual.

Rhinitis and asthma are obvious allergy conditions due to dust and dust-mite. What isn’t so generally known, however, is that it is often the principal cause of eczema. I am grateful to Dr Paul August for calling this to my attention some years ago. He is a very enlightened dermatologist and uses the environmental and allergy approach to try and help his patients. He noted that many eczema patients tend to improve when moved into hospital and wondered if it wasn’t simply because the linen was changed daily, which keeps dust and dust-mite to a minimum. To test this idea, he would ask relatives to bring in dust samples from the patient’s own bedroom and, without saying what he was doing, sprinkle it into the patient’s hospital bed while pretending to examine them. If the rash reappeared within 24 hours, he was able presumptively to diagnose a dust allergy.

Reducing dust and dust mite allergy

As with all allergies, the choice boils down to avoidance or desensitization. Desensitization may be attempted, especially if the allergy is severe, using the low-dose method (Miller’s method). Classic hypo-sensitization (increasing doses) can be dangerous in the presence of a severe allergy and is not recommended. Both are described elsewhere in the book.

Classic and alternative desensitization methods

Avoidance is a good strategy, even if you opt for desensitization. It is impossible to get rid of dust and dust-mite, but reducing it significantly will help the total body burden. Fighting dust is a complicated business, especially in older homes, and the best advice I can give is: do as much as you can or as much as you need to. The more severe the problem, the tougher you will have to be in controlling dust levels.

The absolute minimum is to protect your mattress and pillow with allergy grade covers.

An under-blanket may be used outside this cover but if so this must be washed or changed at least weekly. The excrement of the dust mite is water-soluble and therefore washing of sheets and pillowcases reduces exposure close to zero each time the bed linen is changed. Don’t forget to wash the counterpane, otherwise it will gather dust and usually lies close to the sleeper’s face!

Next would come lifting the bedroom carpet. Replace is with dust-proof flooring, such as linoleum, tiling or cork. If you opt for renovating the existing floorboards, which can be quite attractive, you will have to be very thorough in sealing all the cracks. The space under floorboards may contain centuries of gathered dust. Ugh!

To go further, remove all sources of gathered dust, such as pelmets, curtains, lampshades, bookshelves and open wardrobes from the bedroom. Vacuum clean it frequently, in all corners, no matter how hard to reach, at least once a week. Ideally, the person who has the allergy should not be present in the room at these cleaning times or for some hours afterwards. Get a special vacuum cleaner with an allergy-effective filter; it must screen down to at least 3 microns. Most vacuum cleaners suck up dust and then blow some of it back into the air, through a leaky bag. Vortex cleaners are not allergy-effective unless so stated.

Avoid electric open-bar heaters, convection and especially fan heaters, which all circulate dust. If ducted-air heating is present, it should be blocked off to the room and substituted with a radiator. If there is no central heating, the free-standing oil-filled electric radiators are best.

Ionizers and air-purifiers (avoid those with scented filters) may help. Get a purifier which removes particles down to 0.3 micron. So-called HEPA filtration (high efficiency particulate air) goes down to 0.1 micron, removing all dust particles, mold spores and most bacteria. The extra expense is often worth it. Ultraviolet purifiers are available which are effective against living forms but hardly of any additional benefit against inert particles. Insist on trying the effects of any such product before you buy.

For more on air purification and ionizers, see air air purifiers section.

Finally, there are pesticide sprays on the market with which to treat the mattress and carpet. Those containing methoprene are effective and relatively harmless; the World Health Organization has deemed this substance safe enough to add to drinking water, where there is a risk of infection by mosquito larvae in malarial zones. Be sure the patient doesn’t react to aerosols or do it while he or she is absent from the home at least overnight. Follow the instructions exactly. Another substance I have found useful and non-toxic is concentrated tannic acid, also available as a spray such a Banamite™, which does not require an aerosol propellant.

Note, even after using a miticide spray, you must still vacuum the mattress for several more weeks. It is the excreta that cause the reaction and even when no more is being produced, it still takes some time to get rid of all traces. Spray treatment lasts a variable time and needs to be repeated.


The cause of hay-fever, pollens, was first discovered by Charles Blackeley in 1873, in the city of Manchester, just a few miles from the medical school where I graduated. He sent kites high into the air with sticky plates to monitor levels, saved up pollens and tried sniffing them in winter (he was himself a sufferer) and rubbed samples into his skin, to produce what was a very elegant scientific proof.

Hay-fever is characterized by red, itchy eyes, sneezing and catarrh, but any seasonal symptom, made worse by pollens (for example, wheezing and rashes), is covered by the remarks that follow. Certain pollens can be identified because of the time of year when symptoms become manifest. For example, trees begin to pollinate in March and April, grasses in May and June and flowers from June onwards, though there are exceptions to these very broad generalizations. Sometimes the trigger is not a pollen but a seasonal mold.

This can be a very precise study. For example, I had one patient who suffered from cyclical affect disorder (once known as manic-depressive psychosis, because of the extreme swings of mood, from one end of the spectrum to the other). He was very much better after identifying and controlling his food allergies. But, even after seeing me, he had occasional admissions to mental hospital with a recurrence of his symptoms. It took me several years to notice that these flare ups were taking place every summer, in fact mid-July. I tested him for sensitivity to Cladosporium, using the technique described on page 000, and – bingo! – that was the answer! This mold peaks in the UK around mid-July and the consequences for this man breathing it were unusual and severe

More about molds, later on this page.

Reducing pollen exposure The main problem is that there is nothing you can do to escape the pollen, or even reduce it, as you can with dust. Short of taking continuous antihistamines, with their tiresome side-effects, or isolating yourself indoors for the best days of the year, the problem has to be tackled some other way.

Desensitization will help but there are many pollens to test and unless you identify and treat the right ones, the results will be disappointing. The limitations and warnings given in the section on dust above apply here also.

But there is another helpful plan. A big secret which so intrigued the media that I was asked to broadcast all over the world, live and down-the-line phone interviews, to explain its magic benefits for hay fever sufferers. Predictably, experts scoffed but those who took the trouble to try it discovered it works and I am pleased it is now common for doctors to recommend dietary avoidance to their patients, with or without any other treatment. You can do it by yourself, which is great, but of course this makes some doctors mad as hell!

The secret, once again, is the total body burden. How many people ever think of going on a diet to combat hay-fever? The logic is simple: if you eliminate any food allergies, the body is better able to cope with inhaled allergies. This is particularly true for cereal foods we eat such as wheat, corn, rye etc., and those with allergies to grasses (hence “hay” fever) are especially helped. But avoiding milk, food additives, tea, coffee and alcohol can also have a remarkably beneficial effect. It isn’t a sure-fire cure, but it is certainly worth a try and anything is better than feeling utterly wretched just when everyone else is having all the fun.

Try the simple elimination diet at a time when the pollen count is high. Even if you don’t clear the symptoms, you may reduce your need for medication quite considerably. Don’t forget to follow up the diet with challenge tests, if it works. Find the real culprits.

[Special note: allergy to Betula species (birch) commonly cross-reacts with foods in the nut-and-pip group and may overload. If you have a birch allergy, try the nut-and-pip free diet on the food allergy pages]

The ragweed problem

Ragweed is a nationwide allergy problem in the United States. Very few areas can claim to be ragweed-free. Ragweed, a rampant yellow flowering weed, is a member of the Aster Family. Two species are significant: the giant ragweed Ambrosia trifida and short ragweed Ambrosia aratemisiifolia. These species can flourish on very poor soil and out-compete most other plants, which is why they are so prolific. It is estimated that approximately 100 million tons of ragweed pollen per year are released in the United States alone.

The season runs from late August to early November. If your symptoms are at a peak late September and October, the chances are that ragweed is your problem.

What you can do:

Miller’s desensitization is relatively successful and easy to do, since the likely culprits are known. Read about it in the testing section. If you cannot find a practitioner of this method, you may need to resort to anti-histamines, decongestants and nasal sprays. Try to stay indoors in the peak hours, 6- 10 am. Change your clothing if you have been outdoors and take a shower, to avoid bringing the allergen into your home. Remember pets too can carry a considerable volume of pollen. You may need to keep your pet outdoors for the critical weeks.

Once again, elimination dieting can help. Foods which cross-react with ragweed include honeydew melon, cantaloupe, watermelon, squashes, zucchini, banana, cucumber and chamomile. You may notice that these foods cause symptoms in your mouth, such as itching of the tongue, roof of the mouth or throat. In which case avoid them at all costs.

Finally, change your body from reactive to non- or less-reactive using homotoxicology. If you haven’t already learned of the wonders of this science, go here.


Molds are a serious problem. More food crops worldwide are lost to mold than any other single cause. Yet we need them to rot away rubbish and dead matter Along with certain bacteria, molds clean up organic waste and stop the planet becoming a gigantic garbage heap.

Unfortunately, mold allergies are very common. Drug reactions to antibiotics, such as penicillin, are mold allergies. Most exposures, however come from mold spores floating in the air. Molds are rather like an all-year-round pollen, only absent during hard frost or when the ground is covered with snow.

[Special note: I believe the old wives’ idea of the nose twitching as a sign of coming rain is a well based observation. Mold spores are released in plenty as the air pressure alters prior to a change in the weather and a mold-sensitive individual could well experience nasal irritation!]

Some indoor molds, notably Stachybotrys chatarum – a common black mold – can be very dangerous. Stachybotrys causes lung bleeding in infants. It may even be a cause of sudden infant death syndrome. Stachybotrys has been implicated in a variety of symptoms in adults, including memory loss, disorientation, confusion, difficulty in focusing and personality changes. A little like Alzheimer’s, don’t you think?

Suspect mold allergy if:

  • you are bad on damp, humid days
  • better in cold weather
  • cravings for bread, alcohol or yeast foods
  • damp, musty buildings make you ill
  • you have a skin mold (athlete’s foot, Tinea versicolor, ringworm)

Ringworm, of course, is not a worm! It is a mold which grows outwards from the center and thus has a circular shape, with an active (growing) outer ring. This and other skin fungus growths are called Tinea. The common guilty molds are Trichphyton and Microsporum species.

Any symptom can be caused by mold. Stuffy nose is obvious. But the most overlooked symptoms are mental ones. These can be extremely bizarre and frightening. In medieval times people would sometimes eat rye bread infected with poisonous mold. This resulted in an intense burning of the skin (St Anthony’s fire) and wild, violent and irrational movements (St Vitus’ dance). It has even been suggested that the outbreak of hysteria and hallucination in Salem, Massachusetts, in 1692, attributed to witchcraft, could have been an outbreak of rye mold poisoning; if so, lives were tragically lost due to ignorance of this malady.

I have seen patients acting very strangely on mold challenge tests. One woman shook uncontrollably, from head to toe. Another patient cried for hours, though he explained that he felt fine and definitely not sad or anguished. The trouble is that this distressing manifestation is hardly ever diagnosed because no one ever thinks of it and thousands of patients suffer mysteriously and needlessly.


Mycotoxins are poisons produced by molds. For example the mold Claviceps purpurea, which may contaminate rye, produces dangerous ergot-like substances, which have effects not unlike LSD. Most mycotoxins are present in insignificant quantities and pose no threat to humans. But a few are deadly. These are pharmacological reactions, however, not allergy.

Aflatoxin B1 is a potent liver toxin and carcinogen, secreted by the common mold Aspergillus flavus, which grows on wheat, maize, peanuts and other crops. Many environmentalists regard aflatoxin B1 as the most potent carcinogen known. Millions of tons of foodstuffs are condemned annually, due to contamination by aflatoxin. The trouble is much of the condemned food is fed to animals and the aflatoxin turns up in the flesh we eat. Aflatoxin, like most mycotoxins, survives cooked, so this is not an option for getting rid of them.

Other mycotoxins include ochratoxin-A, produced by some strains of Penicillium mold growing on wet grains. It too can contaminate offal meat. Ochratoxin-A can cause serious kidney damage.

A Fusarium toxin, deoxynibalenol (DON), has been linked indirectly to disorders of the immune system. DON is also known as vomitoxin because it causes pigs that eat it to vomit. Another toxin from Fusarium, zearalenone, has been identified as a cause of abortion in animals. Zearalenone and its derivatives mimic female sex hormones by binding to the same receptor-sites as oestrogen. The chief concern regarding human health is the possibility of such mycotoxins affecting hormone-dependant cancers or producing foetal abnormalities.

It is vital we all protect ourselves against pseudo-oestrogens from the environment. Men are just at much at risk as women; they risk low sperm count and younger boys even risk abnormal sexual development. Fit a carbon water filter as a priority.

Reducing mold exposure

Consider mold problems if your house is low-lying in a damp valley. Older houses are especially suspect, particularly those with a condensation problem. Sometimes it is possible to see the mold growing on the walls and carpets!

You will need professional advice to be sure of getting rid of the damp. It may entail major structural repairs. If the problem is too extensive, you should consider moving, if you value your health. In the meantime, a dehumidifier should help to reduce the damp.

Clean mold wherever you find it, using a dilution of chlorine bleach to four parts of water. Do not soak fabrics and soft furnishings in this process. Moisture is the enemy. Remove all moldy fabrics, once contaminated.

Once again, dieting has considerable value in reducing cumulative overload. Certain foods are actually fungus or molds (mushrooms and cheese). Yeast products are similar and often cross-react. A suitable diet for a mold-sensitive individual would of course avoid these and also foods containing yeast and fermentation products:

  • alcoholic and fermented drinks
  • bread (except unleavened)
  • vinegar
  • sauces
  • malt and malted foods
  • yeasted cakes
  • coffee and chocolate (fermented during processing)
  • B-vitamin products (unless stated yeast-free)
  • over-ripe and moldy food
  • cartoned and bottled fruit juices also contain significant amounts of yeast, but not when freshly squeezed

Remember: that house plants encourage molds which grow in the damp soil. You may need to get rid of them.

Animal hair and danders A difficult subject is the question of animals. Allergies to dogs, cats, horses, birds and other pets can cause severe allergies. The obvious solution – get rid of the allergen – is often refused on emotional grounds. People become very attached to their pets.

If you don’t think you can bring yourself to undertake the ‘logical’ solution, you must do the best you can. Certainly removing other allergens will help.

Keep animals out of the bedroom at all costs. That’s where you spend the largest segment of the day. Under no circumstances let the pet sleep on the bed. Once fur and dander are present, it can be very difficult to get rid of.

Use a vacuum cleaner fitted with an allergy filter to keep hairs to a minimum. Fresh air, of course, will tend to whisk away airborne hairs and danders.

On a cheerful note, trials have shown that cat allergen can be washed out of the fur, so a regular dunking of your beloved pet, while not appreciated by a feline, is good for humans who suffer. Dog hair and dander, unfortunately, is coarser and does not wash out satisfactorily.

Small rodent urine

The urine of small rodents can be a powerful allergen. This isn’t widely known and possibly you have never been told. I am thinking not so much of rats and mice (vermin), but the pets children sometimes keep, such as guinea pigs, hamsters and gerbils. The last two are particularly troublesome since they are often kept in the child’s bedroom.

Fortunately, these animals don’t live long and pronounced attachments are rare. Don’t replace the animal when it dies. Give it away if you can persuade the child. If not, ban it from the bedroom and see that the litter is changed frequently and kept dry.

Beware your child is not unduly exposed at school, where small pets of this type are sometimes a collective item and live in the classroom. The allergy can affect adults, of course, so suspect it if you suffer asthma or similar and your child has small pets. One of my patients was a teacher and she found out about small rodent urine allergy from the effect of the classroom pet on her own health!

One Last Time: always consider the possibility of chemical reactions if you are ill only in certain locations, or breathing certain air, whether it occurs seasonally, intermittently or most of the time. Symptoms may or may not be related to the respiratory tract and can afflict any target organ.

Air Purifiers

If you suffer from airborne allergens (or chemicals), it makes sense to try and improve the quality of the air you breathe. There is nothing to be done about urban pollution, or summer allergens, apart from keeping your doors and windows closed. But there are a number of air purification devices on the market which may help you to produce a clean local environment, whether in your bedroom or at the office.

Some people will find the equipment below very useful, enabling restful nights and symptom-free days, perhaps for the first time; others well benefit only little and find trying to tackle inhalant particles and gases not worth the trouble. People vary and there are no hard-and-fast rules. A little experimentation is recommended. Good manufacturers and suppliers will often lend you equipment on an approval basis, so you have a chance to try it first.

It isn’t realistic to expect to achieve an environment that is 100-per-cent controlled, except in an environmental control unit, which is a medical specialty.

Face masks There are situations where a multiple sensitive person may want to wear a protective mask, for example when cleaning in a dusty enclosed space. However it is not a good idea to get into the habit of using artificial aids on a semi-permanent basis. Often this means little more than psychological dependence that may not have any relation to scientific removal of impurities. Patients who squeal and hold a handkerchief over their face every time someone takes the top off a felt tip pen is inviting ridicule, moreover (my point entirely) there are far better ways of conquering your problem than this.

If you need to use a mask, be aware of the different types and their limitations:

  1. Lightweight, cotton surgical masks strain out particles such as pollen, dust and smoke. People sensitive to wheat and flours who work in the catering industry may need one of these. They are not completely effective against particles.
  2. For chemical vapors you may need an activated-charcoal filter mask. There are many simple versions of this design which, in its full form, is the gas-mask worn by troops in combat. Suppliers claim these are effective against benzene, ozone, diesel fumes, lead salts, hydrocarbons, nitrous oxide and sulphur dioxide. Most people would probably benefit from one of these masks when encountering smog.

Air filters

If you can’t face the expense of major household filtered air purification, consider a small, mobile system. Standards are variable and if possible you should try out a model before buying. Beware of buying a unit that seems inexpensive but is inadequate to the task; check volume air turnover and compare this to the size of the room you are trying to maintain pure. Aim for at least four changes of air per hour.

The best units combine chemical purification (activated carbon) with particulate removal of varying standards (see next 3 sections).

Avoid units with the deplorable addition of scents and ‘fresh air’ perfumes; this adds chemical pollution.

There are portable models for the car that plug into the car’s cigarette lighter socket. Used properly these may assure that you arrive in a refreshed state after a long drive, instead of semi-drugged with traffic fumes!

Activated carbon filters

These are fairly effective at absorbing cooking and food smells, cigarette and tobacco odors, perfumes, diesel and petrol fumes, smog, ozone and animal smells. They are less effective against pollen, smoke, mildew, chlorine, fish odors and some noxious gases. Unfortunately, they perform poorly against two dangerous indoor chemicals, carbon monoxide and formaldehyde.

Electrostatic air cleaners

A fan draws in particles and these are then given an electric charge that causes them to stick onto a screen or plate. Manufacturers claim they remove 90 per cent of particles. In fact performance falls off very rapidly and within days the unit may be less than 50 per cent effective. This type of purifier also needs constant cleaning and maintenance.

Another problem is that charged particles that ‘escape’ the screen or plate and stick on walls and furniture. There can be considerable build up, which causes discoloration. This type of filter may also produce ozone, a highly toxic gas that causes headaches in susceptible people.

High efficiency particulate air (HEPA) filters

These are over 95 per cent efficient for particles down to about 0.1 micron in size (see particle chart), according to the US National Bureau of Standards. Predictably they are also quite expensive. They are sometimes called absolute filters and are used to maintain sterile air in hospital operating theatres and burns units.

HEPA filters work particularly well against important sensitizing allergens such as pollens, moulds, yeasts, fungi and bacteria. They are also effective against viruses, which means they may help to cut down on colds and other infections.



It has been observed that people often feel better and more zestful when they are near mountain streams or beside the sea. At least one possible cause for this is the presence of excess negatively charged ions in theses places.

The earth is positively charged and so attracts these ions, yet they tend to be diminished in buildings such as homes and offices. In fact, for comparison, the average negative ion concretion near a waterfall is 50,000 per cubic centimeters, in mountain air 5,000 and in the countryside 1500 or so; yet in a modern office, this figure can fall to as low as 50.

What happens to the ions in buildings? They are electrically precipitated by particles in the air, notably dust, cigarette smoke and fabrics such as synthetic carpet fibers. Modern closed ventilation systems and of course the ubiquitous office computer make the problems many times worse. Because of the static build-ups.

Accordingly, therefore, it seems a good idea to try and supplement your environment with negatively changed ions. This is done by means of so-called ionizers. Studies are poor to date but at least one trial carried out by an insurance company in the UK using ionizers ‘double-blind’ showed a remarkable 78 per cent drop in the incidence of headaches and other minor symptoms.

The atmosphere in ionized spaces is generally cleaner and ‘feels fresher’ because there is an increased rate of precipitation of particulates, thus reducing cigarette smoke clouds and circulating dust. The potential benefits for allergic patients seem obvious.

Additionally, ionize may remove harmful bacteria from the air. Since droplet spread from exhaled breath is a potent method of cross-infection, this may mean less illness. ionizers trials in a Swiss bank reputedly showed a dramatic fall in absenteeism due to coughs, colds and other infective complaints.

However, a note of caution must be sounded amongst the enthusiastic claims that manufacturers make. Mains–operated ionizers generate adverse electromagnetic fields pulsating at 50 to 60 Hertz. Some individuals will be highly sensitive to these fields. At least one of my patients did a blind controlled trial study with his ionizer. His wife would switch it on only on certain heights, without telling him which. It didn’t take long for them to realize that on the nights when the machine was switched on he had angina-like symptoms and felt quite ill. Indeed at one point he felt ready for hospital. So the effects are not always necessary beneficial.

As with so many environmental considerations, individual experimentation is called for.

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