The Segal Guide to Asthma

Michael Segal MD PhD

Asthma is a disease that results in difficulty breathing as a result of inflammation inside the breathing tubes in the lungs.  The incidence of asthma has been increasing dramatically in recent decades, as outlined in a New York Times article and a New England Journal of Medicine article.

Some of the increase may be due to an increase in susceptibility to asthma and some of the increase may be due to increase exposure to substances that trigger asthma.  Although much remains to be discovered, we can reduce the effects of asthma by avoiding the triggers of asthma episodes, building up resistance to these triggers, and if necessary, treating asthma with medications.

Take precautions with cooking or fire

One of the more common triggers of asthma is cooking or fire, creating problems in 3 different ways: smoke, nitrogen dioxide, and volatile organic compounds.


The danger of smoke are well appreciated, in part because smoke is one of the few asthma triggers that are visible.  Children are much more likely to experience asthma if there is a smoker in the household.  It is crucial that members of the household of a person with asthma do not smoke.  Avoiding cigarette and pipe smoke in public places is also very important.

Other sources of smoke in the house are also a problem.  Matches are a particular problem since they contain sulfur compounds that burn to form sulfur dioxide, a pollutant that severely aggravates asthma.  If you need to light a candle or another flame, a butane lighter is a better solution.  Avoiding smoke from stoves and fireplaces is also very important. Broiling and toasting of food produces smoke, so it is important to have proper ventilation as described below.  Barbecuing outdoors solves the ventilation problem as long as nearby windows are closed to keep smoke from getting inside.

Nitrogen dioxide produced by flames

There have long been concerns about natural gas stoves triggering asthma.  The asthma-triggering pollutant appears to be nitrogen dioxide, not from the natural gas itself but from the flames heating the nitrogen and oxygen in air.  In an airtight kitchen, levels of nitrogen dioxide from a gas stove rise to unsafe levels within minutes.  In the lungs, nitrogen dioxide produces free radicals and nitric acid, irritants that makes breathing difficult, particularly for people with asthma and emphysema.  The irritation comes on with little warning because nitrogen dioxide doesn’t produce as obvious nasal symptoms as do allergy-based asthma triggers such as perfume.

The science is highly suggestive of natural gas stoves being a problem in homes, but not 100% settled.  Studies claim that in 13% of children stoves are the main trigger of asthma, and in 54% of children they are an important factor.  However, in the largest of the epidemiological studies about asthma and natural gas an international collaboration found no effect of gas stoves on asthma, though the authors note that the study had a “major limitation” in not having “information about kitchen ventilation”.

It appears that gas stoves are safe if there is proper ventilation as described below. 

Volatile organic compounds released from food or wax being heated

Cooking using certain types of food oils vaporizes volatile organic compounds, often from oils.  Some oils such as olive oil are particularly likely to release volatile organic compounds even at low heat, but other oils may be problematic because they aerosolize particular proteins in the oil that are allergens. 

Candles can be a problem due to all 3 factors, smoke, perfume in the candles, and nitrogen dioxide.  If you need to use candles (e.g. religious ceremonies), you can reduce the smoke problem using "hurricane glass" enclosures, a decorative accessory that protects the candles from drafts and ensures a constant up-flow of air around the candle, and using proper ventilation while the candles are still burning. 

Proper ventilation

The importance of ventilation to remove asthma triggers in the air may seem obvious, but in the real world, it is often not done adequately.  Windows are not always open, and most people turn on ventilation only when cooking is producing smoke because many people don't know that burning natural gas in itself or heating cooking oil can trigger asthma.  Worse yet, some ventilation systems merely recirculate the exhaust back into the kitchen after going through activated charcoal, which removes much of the smoke but doesn’t remove nitrogen dioxide.  It is crucial to have ventilation that vents to the outside. 

Avoid allergens and irritants

Avoid perfume and perfumed household products:

Perfumes can be very potent in triggering asthma.  A typical perfume contains tens to hundreds of volatile organic compounds.  Such compounds were originally discovered in natural products such as flowers or fruits, but now most perfumes are manufactured from synthetic chemicals.  Both naturally-produced and synthetically-produced perfumes release into the air many volatile organic compounds, some of which can trigger asthma.  The asthma risk is present regardless of whether the compounds were produced naturally or synthetically.   

It is not yet clear from publicly available information which ingredients in perfume are responsible for the asthma.  Some of the volatile organic compounds found in perfumes are believed to have adverse health effects (although some of this information at that site is from Material Safety Data Sheets, which are often unreliable). Indeed, it is likely that many of the compounds in perfumes will turn out to be safe.  However, the problem is that each perfume contains a large number of ingredients and a few of these ingredients may trigger asthma.  Unfortunately it is not possible to predict the asthma-causing properties of a pure chemical or perfume mixture from its smell, so one is not necessarily safe with perfumes that lack a strong smell.  Although in the future asthma problem from perfumes will be reduced by manufacturing perfumes using mixtures of ingredients shown to be safe for people with asthma, such efforts have not been undertaken on any significant scale yet.

People with asthma should be very careful about wearing perfume themselves, doing so only after careful testing of a particular brand.  For children with asthma it is particularly important to make sure that parents and child care workers avoid using any perfume unless there is clear evidence that the child is not sensitive to the particular perfume being used. Parties at which perfume is worn can be a big problem for people with asthma.  Since it is virtually hopeless to try to advise partygoers against using perfume, parties may be an occasion for using medications just before the event to reduce the effects of allergens (see below).

Over the past few decades perfumes have expanded from being personal adornments to becoming additives in a large number of household products.  Many products now come in "standard" perfumed versions and "special" more expensive versions with no added perfume.  Avoid the "standard", i.e. perfumed versions.  Products that often contain asthma-triggering perfumes or solvents include soap, dishwashing liquid, laundry detergent, fabric softener, paper tissues, paper towels, toilet paper, shampoo, hair spray, hair gel, cosmetics, facial cream, sun cream, deodorant, cologne, shaving cream, aftershave lotion, air freshener and candles.  Products such as oil-based paint can trigger asthma as well.  Even one such product in a household can result in a significant increase in asthma symptoms. There are anecdotal reports of households in which removal of a single product such as a scented laundry detergent produced a sharp decrease in nasal congestion, asthma and bronchitis.  The amount of perfume used in household products has increased dramatically in the last several decades possibly accounting for some of the dramatic rise in asthma symptoms and deaths over the same period.

There is very low awareness in the general public about the hazards of perfume, due in part to the hazard being invisible and to the fact that the mixtures of organic chemicals in natural and synthetic perfumes are very complicated and protected by trade secret laws.  Many hospitals have policies against the use of all perfumes and other fragranced products by employees prompted by incidents of asthma patients worsening after exposure to perfume.  

Avoid indoor dust:

Indoor dust contains general irritants as well as specific allergens such as dust mites, cockroach parts, human skin and animal fur particles.  Recent studies have shown conflicting results as to how important dust is in triggering asthma, but it is prudent to keep a home well vacuumed, using bags with enhanced filtering capabilities if they are available.  Keeping a house dust-free is easier to do if there are few surfaces such as carpets and drapes that retain dust, though some argue that carpets trap dust and prevent it from flying around. The person with asthma should not be the one to do any activities likely to generate indoor dust such as vacuuming, unless there is no alternative, and then a high quality mask should be worn.  High quality N95 masks work very well if there is a good seal that prevents flow at the edges of the mask (good nose fit, no beard).  Masks with exhalation valves such as the 3M model 8511 are ideal because the chief breathing problem in asthma is on exhalation.

Forced-air heating is often harmful because it spreads around dust.  However, equipping a forced air system with an electrostatic precipitator, which traps small particles, combined with a mechanical filter, which traps large particles, can actually improve the dust situation.

Avoid fumes from cleaning products

Many cleaning products such as chlorine bleach produce gasses that irritate the lungs and trigger asthma episodes.

Use a mask for exercising in very cold weather:

Exercise-induced asthma is thought to be triggered by dehydration within the lung caused by the low relative humidity of very cold air warmed to body temperature.  Wearing an N95 mask with an exhalation valve largely prevents this, making exercising outdoors with a mask actually easier than without a mask. 

Use a mask for high pollen conditions:

Allergens can trigger asthma by a direct effect on the lung or indirectly by triggering rhinitis.  Wearing an N95 mask with an exhalation valve can reduce this exposure substantially and reduce asthma symptoms.

Avoid animal fur and saliva allergens:

Animal fur or cat saliva are common triggers of asthma. People with asthma should give very serious thought to not having cats or other furry pets, since these commonly trigger asthma.  Cat saliva can be so persistent that it still causes symptoms after carpets have been washed several times.  This persistence of cat saliva makes it difficult to eliminate the effect of the allergens it contains, and even makes it difficult to test whether a person is sensitive to the presence of a cat except by leaving the premises.

Reduce the effect of allergens and irritants

Use steam showers to clear allergens and mucus out of the lungs:

Steam showers are one of the best ways to remove irritants from the lungs, as well as remove products of inflammation such as mucus.  The steam helps remove this material by moistening it and making it easier to cough it out, and may also reduce the amount of smooth muscle that can block off air passages.  To produce the steam you can use a shower of very hot water directed away from yourself, but a better approach is to have a steam generator installed in the tub enclosure.  This not only gives more steam, but there is less danger of scalding and drying of skin, and far less energy and water are used.  The best way to retain the steam is to use an enclosed bath or shower stall.  This not only avoids wasting steam, but it also does not let the steam out to ruin the paint on the bathroom ceiling and walls. 

Since upper respiratory illnesses (head colds) are one of the most common triggers of asthma episodes it is particularly important to take steam showers if such symptoms have started.  The steam may have additional effects in killing cold viruses in the mouth.  At times when one has a head cold, it may be helpful to take as many as two or three steam showers a day.

Get vaccinated against pneumococcal pneumonia

The Centers for Disease Control and Prevention recommends that people with asthma get vaccinated against pneumococcal pneumonia because of the danger of asthma complicating pneumonia and bronchitis.

Use steroid sprays if necessary:

Steroid sprays are one of the best treatments for asthma. They reduce the inflammation produced by irritants such as perfumes, smoke, or cold viruses.  It is best to prevent the irritation in the first place, but in practice it is difficult to remove all irritants such as smoke, cooking vapors or perfume from the air everywhere you go.

Steroid sprays are only available by prescription in the USA. Although the main studies of steroid sprays were done using regimens lasting weeks, it appears that steroid sprays may take effect in minutes to prevent inflammation, or in hours to treat inflammation. It may be reasonable to use a steroid spray before a party in which someone nearby could be wearing perfume or smoking, or before a meal at someone else's house if they have poor ventilation and have a gas stove.  It is often recommended that people who develop asthma with head colds should use the steroid spray as soon as the cold symptoms begin.

Use antihistamines if necessary:

Antihistamines can also be helpful in preventing the effects of allergens that cause release of histamine, which produces part of the phenomenon of asthma.  Many people with asthma use antihistamines during pollen season, though there are concerns that the body compensates in ways that reduce the effectiveness of long-term use. The most convenient antihistamines are those that are non-sedating. 

Use leukotriene receptor antagonists if necessary:

A group of drugs called "leukotriene receptor antagonists", including monteleulast (Singulair), can be very helpful in asthma.  Leukotrienes are produced within the body and released following exposure to allergens, and are up to a thousand times more potent than histamine in producing asthma.  It appears that a sub-group of asthma patients respond very well to these drugs, while others benefit far less.  However, there can be serious side effects that resulted in an FDA "Black Box" warning about neuropsychiatric issues.

Build up resistance to asthma

Exercise even if that causes wheezing:

Many people with asthma have exercise-induced wheezing, so they are often advised not to exercise much.  However, such advice can be counterproductive because regular exercise builds up resistance to asthma symptoms.  Exercise can also help clear mucus from the lungs.  Although exercise will lead to some wheezing, this is transient and the likelihood of wheezing at periods such as the middle of the night or an allergic reaction to food may be reduced.

Avoid artificially reducing resistance to asthma

Try to avoid the epinephrine-like group of drugs:

Drugs such as albuterol (Ventolin) and metaproterenol (Alupent) are very commonly prescribed for asthma. These drugs are similar in their actions to epinephrine, a signaling molecule that the body uses in emergencies, acting to open up breathing passages. Using these epinephrine-like drugs, usually as inhaler sprays, opens clogged breathing passages in the lungs. This reduces wheezing in the short run very effectively, and appears to reduce the base rate of wheezing in most people. However, the lungs adapt to these drugs, and this may reduce the body's ability to protect itself in certain circumstances.

People with asthma who take these epinephrine-like drugs are more likely to die of asthma than people with asthma who do not take these drugs. It is possible that this increased mortality is merely a reflection of the fact that people on these medications have worse asthma than those who do not take the drugs.  However, it appears that the body adapts to these drugs since the asthma reaction produced by experimentally-administered histamine worsens after chronic use of these epinephrine-like medications.  It appears that the chronic adaptation of the lungs to the drugs reduces the ability to recover breathing ability following a surge in the body's natural epinephrine or from epinephrine given as an emergency injection.  It is therefore possible that use of these drugs might actually be contributing to the increase in asthma deaths over the last several decades.

This adaptation of the lungs to epinephrine-like drugs may be a particular problem for people who also have food allergies. During an allergic reaction, the epinephrine produced by the body or given as an injection is the most important line of defense against life threatening asthma during the allergic reaction.  A person taking epinephrine-like drugs has become adapted to the effects of epinephrine.  People who die during allergic reactions have usually been taking these epinephrine-like drugs.  The increase in asthma and allergy deaths in recent decades has occurred despite the widespread introduction of powerful epinephrine-like asthma drugs.  It is controversial whether the rise in deaths is related to the widespread use of the epinephrine-like drugs.  There are clearly other possible explanations, but many doctors and researchers are concerned about the epinephrine-like drugs, even the long acting ones.  In the meantime, it may be best to try to avoid using the epinephrine-like the drugs if possible.  However, do not discontinue these medications abruptly because the lungs can become dependent on the stimulation from these drugs for the ability to breathe properly.  Once off these drugs, it is probably best to be very wary of using them again unless one is in severe distress.

Try to avoid the caffeine group of drugs:

Caffeine-like drugs such as theophylline have been used to treat asthma, but such drugs may worsen asthma in the long run by leading to a dependence state.  Such an effect of these drugs has been best studied for headaches, where caffeine has a short term effect of reducing the severity of a headache but produces a headache when caffeine levels are falling.  For asthma, this effect can be very problematic; the caffeine wears off typically in the early morning hours when the drug has not been consumed recently, exacerbated by the tendency to have less caffeine towards bedtime to avoid interfering with sleepiness. As with headaches, people with asthma can do best by following a strategy of avoiding caffeine-like substances.

Avoiding caffeine-like substances is very difficult for many people at first.  It means avoiding medicines with caffeine or theophylline, and avoiding large quantities of chocolate, caffeinated coffee, tea and soft drinks.  A good test to see if these caffeine type products affect your asthma is to avoid consuming them for a few weeks, and then have a lot of coffee or chocolate one day.  If you have relief of symptoms in the first day followed by worse symptoms the next day, you probably have some dependence and withdrawal effects, and you should think very seriously about staying off these caffeine-like substances.  For people whose asthma is exacerbated by stomach acid irritating the lungs, avoiding caffeine is also helpful by reducing stomach acid.

Avoid margarine

One study has found that "eating lots of margarine doubled the risk of asthma and allergic rhinitis".  The details are unclear, but for this and other reasons it is prudent to avoid margarine.


This series of suggestions probably seems quite daunting.  However, in practice the recommendations are less trouble than one might imagine in one's own home because most of the suggestions are to avoid certain triggers of asthma. Once you have gotten accustomed to avoiding certain things and feeling better, the temptations of perfume, smoky rooms or even large quantities of chocolate are reduced. However, be prepared for the possibility that some child-care employees will prefer to work somewhere else rather than avoid wearing perfume in your home.

Outside your home or when having guests in your home, some temporary minimalistic precautions are often needed.  When visiting another home for a few hours, it makes sense to ask that proper ventilation be used when cooking if you will be anywhere near the kitchen. When having guests to dinner, it makes sense to ask them not to wear perfume or bring flowers.  most people will be understanding about such minimalistic precautions, and since about 8% of the population has asthma, such knowledge is useful more widely.

Dr. Segal is a physician who has asthma.  Copyright 2002-24 Michael Segal