Pollens are the male sex cells that grow on the stamens of flowers. Plants that have readily recognizable attractive flowers usually contain heavy sticky pollen that is transmitted by insects. This kind of pollen causes little respiratory allergy. It is wind-born pollen from plants that have inconspicuous flowers like wild grasses or ragweed that are the major causes of respiratory allergy. They are microscopic in size, invisible singly to the naked eye. These pollens, produced in vast quantities, are designed to carry far distances. Your exposure is therefore not dependent on what is growing in your yard or even your next door neighbor's yard. The vegetation for many miles upwind provides you with exposure to pollens from plants that you never see. Pollens are regional, however, and your exposure will be different in different geographical areas. There is no practical means to limit exposure to pollens outdoors. However, at least half of a 24-hour day is spent indoors, and air conditioning with high-efficiency air filtration can markedly decrease indoor exposure. For these to be optimally effective, the building must be reasonably well sealed and have a continuous central air circulation system so that air is continuously filtered, not just when the air conditioner condenser (or heater) turns on. Most forced air home furnace/air conditioners have continuous fan operation as an option. There are various types of high-efficiency air filters. Discuss with a heating contractor which would be most suitable for your home.

Outdoor molds (Alternaria, Hormodendrum, Epicoccum, Cladisporum, and others) grow predominantly on decaying vegetation. They give off microscopic spores that are the "seeds" from which new molds grow. The type and extent of outdoor molds vary with the climate. In temperate climates, they are seasonal with variable concentrations in the air during the growing season. They may not be as much of a problem in dry climates such as the Southwest U.S. While exposure is likely to be influenced by the mold growth for miles upwind, increased exposure can occur from local conditions such as extensive decaying vegetation (as in forests) or when the ground vegetation is disturbed (as when mowing a lawn). There is no practical means to limit outdoor exposure to molds. However, at least half of a 24- hour day is spent indoors, and air conditioning with high-efficiency air filtration can markedly decrease indoor exposure. For these to be optimally effective, the building must be reasonably well sealed and have a continuous central air circulation system so that air is continuously filtered, not just when the air conditioner condenser (or heater) turns on. Most home furnace/air conditioners have continuous fan operation as an option. There are various types of high-efficiency air filters. Discuss with a heating contractor which would be most suitable for your home.

Household pet dander frequently contributes to symptoms from inhalant allergy. The dander is microscopic particles of dead skin (not the hair itself). The saliva of the animals also appears to have the allergenic substance. The microscopic particles of dander and dried saliva become airborne from circulating air in the home. Short-haired animals are therefore not necessarily less of a problem than long-haired animals, and even hairless breeds are not immune from causing allergic problems. There are suggestions of some species differences so that individuals sometimes report sensitivity to one breed of cat or dog but not another. Since there is no testing material specific for all of the different breeds, this question cannot always be critically examined. The animal itself need not be present for allergic symptoms to occur since the microscopic particles of dander and dried salivary material may still be present in the animal's absence. In fact, it may take months or years for the animal dander to be eliminated from the furniture, carpeting, and forced air circulation system of a home. Exposure to animal dander outside of the home is often less of a problem because the exposure is not as continuous and intense as when the animal lives in the house. Animal dander can be brought into a home from an outside animal by contact with clothing. If the patient is sufficiently sensitive, control measures may be necessary to prevent animal dander on the clothing from contaminating the house.

Horse dander is not commonly seen anymore as a household allergen. The extensive use of synthetics has largely replaced horse hair for upholstering and manufacturing of carpet pads. Quality furniture formerly used horsehair stuffing, and this may still be present in some antiques. Felt pads for use under carpeting were made from horsehair and are still used by some oriental carpet buffs. If sensitivity to horsehair is judged clinically important and horsehair is present in these forms, reupholstering with synthetic stuffing material and replacement of felt with foam pads eliminates this source of problems.

Housedust is a mixture of material that varies somewhat from house to house and perhaps even from climate to climate. A major component of allergic housedust has been identified as coming from a microscopic insect called Dermatophygoides, known more commonly as the dust mite or human mite. These mites or their feces (mite dung, mite fomite) permeate upholstered material (mattresses and furniture) and carpeting in homes. The microscopic insect and dung particles then become airborne from normal household activities (such as sitting or lying on a mattress or upholstered furniture), and are recirculated by a forced air furnace. High humidity enhances their growth (they appear not to survive under conditions or low humidity). Home humidifiers should therefore be avoided or used only at a low setting if felt to be essential for comfort, for those with house dust mite sensitivity. Completely eliminating exposure to housedust is difficult. Since the most intimate exposure to housedust mite occurs in bedrooms, especially from mattresses and pillows, it is sensible to begin control efforts there. Airtight zippered encasings are available from various sources. Avoid plastic because of discomfort and their tendency to tear quickly, thus decreasing their usefulness. There are excellent special cloth encasings that are impervious to the microscopic particles that can cause allergy and yet still "breathe" sufficiently to provide comfort. Pillows (if not encased) and stuffed toys should be machine washable synthetic and should be washed in hot water at least monthly. Other measures for decreasing dust mite exposure include the simple elimination of obvious dust catchers such as long-term storage in the actively used portion of the house, particularly the bedroom. Synthetic material for drapes, bedding, and carpeting are easier to clean and accumulate less dust than wool. Removing carpeting will further decrease dust mite exposure, but this is more disruptive and the potential value should be discussed with your physician. Cleaning forced-air furnace ducts may also help decrease airborne recirculation of dust, as may high-efficiency air filtration. There are various types of high-efficiency air filters for central furnaces, including some low cost electrostatic replacements for the usual disposable filters on most forced air furnaces. Discuss with a heating contractor which would be most suitable for your home. Room air filters have generally not been found to be clinically useful.

Indoor molds (Penicillium - the common bread mold, Aspergillus, and others) are almost universal to some extent. Their growth is encouraged by high humidity (home humidifiers are best avoided for mold sensitive patients; if used, they should be kept on low settings) Damp basements with water leakage or condensation become particular breeding grounds for the indoor molds. Their growth is further stimulated by high humidity and indoor plants. Live Christmas trees appear frequently to trigger symptoms in moldsensitive patients. The molds cause respiratory allergy from the release of microscopic spores which are the seeds for new molds. These can be recirculated by forced air furnaces. Vigorous cleaning, special moisture control measures, and dehumidification, along with minimizing indoor plants, can decrease mold exposure. However, it is sometimes difficult to eliminate intense mold exposure in old musty homes without extensive renovation.

Smoking and second-hand smoke exposure can contribute substantially to asthmatic symptoms. Smoking for an asthmatic is particularly self-destructive. Not only is the asthma more likely to be difficult to control, but also there is evidence that asthmatics are more prone to the airway destructive effects of smoking that lead to COPD (chronic obstructive pulmonary disease with chronic bronchitis and emphysema). The smoking patient is therefore multiply exposed to risk: the risk of the asthma, the increased risk of the medications used because more are likely to be needed, and the increased risk of developing a second obstructive lung disease in addition to the asthma. This is in addition to the routine risks of lung cancer, cardiovascular disease (heart attacks and strokes), and effects on unborn children during pregnancy associated with smoking. Second-hand or passive smoke exposure occurs when nonsmokers breathe the sidestream smoke created in indoor environments from the presence of smokers. Children of smoking parents have more respiratory illness than children of nonsmokers, and children of asthmatics have more asthmatic symptoms and more emergency room visits for asthma than otherwise similar asthmatic children of nonsmoking parents. Smoking in front of a child with severe asthma (even if asymptomatic at the time) can, with current knowledge, be considered a form of child abuse. Giving up smoking is difficult but not impossible. Not smoking in front of someone who has asthma may be inconvenient, but it is the minimal humane behavior if living with an asthmatic. Patients and parents of patients with asthma should be politely assertive in requesting smokers to refrain from that practice in the presence of an asthmatic.

Fireplaces or wood burning stoves appear to aggravate asthmatic symptoms through direct irritation of the airways from particulate matter released into the air.

Other types of environmental exposure that can cause airway symptoms range from specific types of allergic factors such as wood dusts to nonspecific irritants such as paint fumes. The examples of each are many and varied. Report any unusual types of exposures that you suspect may cause symptoms to your doctor for further assessment.

Moving to escape exposure to inhalant allergens is a strategy often considered but only occasionally carried out because of the economic and social disruption entailed. Before even being considered, however, you should have reason to believe that the benefit will be worth the cost. The potential for benefit can be judged to some extent by the nature and extent of the environmental factors affecting the asthma. Someone with severe asthma and indoor mold sensitivity living in an old musty home with a damp moldy basement heated with open fireplaces and a wood stove is likely to benefit simply from a move to a newer dryer home with baseboard (rather than forced-air) heating. A patient with severe grass pollen sensitivity causing seasonal asthma in Northern California is likely to have far fewer symptoms in parts of the country where grass pollen is less of a problem. On the other hand, there is virtually no ragweed pollen in Northern California, and patients with that sensitivity from other parts of the country are likely not to have that problem in California. Similarly, those who suffer from seasonal outdoor mold sensitivity that causes severe seasonal asthma in much of the Midwestern farm belt will be likely not to have those symptoms in the desert areas of the Southwest. Unfortunately, many who move to Arizona or other areas in the Southwest continue to have much the same symptoms. Before considering a move, discuss with your physician the likelihood of improvement from the change in environment.

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