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Hayfever, or allergic rhinitis, can cause serious complications in cases where other disorders are also present. Researchers acknowledge that there is a recognised link between hayfever and asthma. Once the allergens that cause hayfever reach the lungs, they can cause the chronic lung disease known as asthma and the increased prevalence of asthma these days has drawn attention to this connection.

Asthma is a more complicated condition than hayfever. During an asthma attack the muscles lining the bronchi (the small airways of the lung) constrict and swell, making breathing difficult. Asthma can be treated effectively when diagnosed early but it can be potentially life threatening if left uncontrolled. Approximately 15 million Americans have asthma and it has been estimated that nearly 4000 Americans die from asthma annually.

During an asthma attack, a sufferer may experience wheezing and a shortness of breath, dry coughing, tightness in the chest, and difficulty breathing. An acute asthma attack may make speaking difficult and produce feelings of suffocation. Exposure to certain types of mould spores can also cause allergic bronchopulmonary aspergillosis, the symptoms of which resemble severe inflammatory asthma. This only occurs in a minority of people with asthma but symptoms include wheezing, low-grade fever, and coughing up mucus plus or brown-flecked masses.

Because pollen allergens can trigger both hayfever and asthma, there is some overlap between the two disorders. The link between the two has often been underestimated. Some people who go on to develop asthma already have nasal disorders like allergic rhinitis that has gone unnoticed and untreated. They think that they are just catching cold after cold or have a constantly dripping nose when in fact they have hayfever. The risk is that an allergy attack may provoke a life-threatening asthma episode.

A significant number of people with hayfever have, or go on to develop, asthma. About 15 to 20% of those with allergies go on to develop asthma, a percentage that is significantly higher than the 3 to 5% asthma rate for the general population. It is estimated that between 80 to 90% of people with asthma develop allergies prior to this. This includes hayfever, which is seasonal, and perennial rhinitis, which affects sufferers all year round. The specific statistics for allergic rhinitis patients estimate that between 20 to 38% of them are also asthmatic. In published reports from the past 30 years, it was observed that up to 85% of patients with both asthma and rhinitis recalled having nasal symptoms that either preceded or started at the same time as their asthma. To illustrate this, a study involving around 700 students from Brown University discovered that those who had symptoms of allergic rhinitis when they started at the University, but still no symptoms of asthma, were about three times more likely to develop asthma during the following 23 years.

The World Health Organisation (WHO) studied the impact of allergies on asthma and concluded that if nasal allergies are treated correctly from the very beginning then they can be effective in preventing asthma. Even if a child already has asthma, the proper treatment of their nasal allergies can help prevent the condition from worsening. The tissues in both the nose and the lungs share the same anatomy and histology. They are also exposed to the same airborne allergens and irritants so it makes sense that successful treatment of hayfever can reduce asthma symptoms.

Research suggests that people who suffer from both hayfever and asthma will exhibit more debilitating chest symptoms than patients with asthma alone. Sufferers of both conditions are more likely to wake up at night with asthma, experience what is categorized as "moderate to severe asthma", or miss time at work due to asthma attacks.

It has been suggested by researchers that the incidence of bronchospasm, the tendency of the bronchial tubes to constrict, may be an indicator of the onset of asthma. They have even hypothesized that asymptomatic bronchial hyperreactivity may represent an intermediate phase in a progression from nasal allergies to clinical asthma.

Another theory is that the nasal blockages caused by allergic rhinitis may result in a sufferer relying more on breathing through the mouth. Because the mouth does not have the same filtering system as the nose, the lungs are exposed to more allergens during this type of breathing. Clinical studies during which asthmatic patients exercised while only breathing through the mouth demonstrated that the chances of exercise-induced bronchospasm were dramatically increased. Also, by breathing through the nose, the air becomes warmed and moisturized before reaching the lungs. If cold air is breathed through the mouth, the cold air decreases lung capacity, in conjunction with a cooling of the trachea.

Postnasal drip may have a role to play in the connection between hayfever and asthma. People with chronic allergic rhinitis that causes a lot of postnasal drip often complain that this can produce bouts of coughing and wheezing. While these people sleep, a large number of inflammatory chemicals, including histamines, are often secreted in the upper airways. As this material drips down the throat and into the lungs, it may have a detrimental impact on asthma by causing the lower airways to become inflamed.

Particular living and working environments can have a lot of impact on a person's asthma. The best therapy for asthma is usually to avoid things that cause asthma symptoms, including allergens such as house dust and irritants like cigarette smoke. Irritants are different from allergens in that they do not trigger allergies in the same way as allergens but still aggravate the nose and airways. This means that irritants can still trigger asthma attacks. Irritants include things like smoke, cooking fumes, paints or varnishes, coal dust, talcum powder and pungent odours.

Any of the following can trigger an asthma attack. Irritants such as cigarette smoke, chemical fumes, strong perfume or odours can induce an asthma attack. Viral infections including colds and flu can also cause problems, as can physical exertion or emotional stress. The weather has a part to play, with strong, windy weather or changes in the weather, including temperature, humidity or barometric pressure, that bring particularly cold or dry air, all having the potential to trigger a person's asthma. Allergens like pollen, mould, animal dander, and food, which produce the symptoms of hayfever in sufferers, can also generate asthma. So can house dust, which may contain allergens such as dust mite debris or cockroach droppings. Other, more specific, asthma triggers include aspirin and sulfite-treated food.

An accurate diagnosis of asthma is typically required to determine an appropriate individualized treatment programme for someone with asthma. It has been observed that many parents realize that their children have asthma before their doctor does. Specialists in allergy/immunology have the special skills required to determine precisely what may be the cause of a patient's asthmatic condition. This could be pollens, moulds, animal dander, dust mites, or work place factors. If the asthma is chronic and occurs during all seasons, then the cause may not be related to airborne allergens. Asthma can be triggered by delayed pattern food allergies. Diagnosis of asthma, however, can be quite complicated. Typically this would include a physical examination, discussion of the patient's medical history, lung function studies and selective allergy skill testing. If additional evidence is required, this may include home and workplace evaluations, blood tests and sinus or lung x-rays.

There can be other complications from allergic rhinitis, apart from asthma. The inflammation of the sinus cavities, known as sinusitis, may result. Nasal polyps, small outgrowths of the mucous membrane of the nose, can develop over time. Secondary infections of the ear, larynx and bronchial tubes are other potential problems related to allergic rhinitis. In extreme cases, prolonged mouth breathing by children who experience all-year round nasal stuffiness can possible result in changes in the facial bone growth of children.

Clinical trials suggest that second-generation antihistamines, such as loratadine and cetirizine, are both safe and effective for use by patients with asthma. They relieve the symptoms of both hayfever and asthma, and tests show that patients taking these medications demonstrate improved lung function. So by treating hayfever effectively, you can also alleviate the symptoms of asthma.