Allergic rhinitis, or hay fever, is a condition due to allergy that mimics a chronic cold.

THE nose is an important structure of the body. Apart from aesthetics, it is an organ of smell and it is through the nose that air gets into the lungs.

Air is filtered, humidified and warmed in the nose. During this filtration process, foreign particles and pollutants are removed. These processes ensure that lung function is optimal.

Allergic rhinitis

This is a condition in which the nose produces a response to an allergy-producing substance (allergen). The body recognises the allergen as a harmful substance and produces antibodies, which are proteins the body produces to fight off harmful viruses and bacteria.

When the allergen comes into contact with the inside of the nose and throat, an antibody called immunoglobulin E (IgE) is released. IgE causes the release of chemicals like histamine, leukotrienes, and prostaglandins, which together, cause the symptoms of allergic rhinitis.

The inside lining (mucous membrane) of the nose swells and blocks the airway. This causes congestion and excess mucous production and gives rise to sneezing and runny nose. Other symptoms include itchiness and watery eyes. Most of these symptoms are due to histamine.

Allergic rhinitis is a common condition worldwide. It is estimated that about a quarter of people have allergic rhinitis at some stage in their lives.

Some people get allergic rhinitis at particular times of the year because certain allergens are produced seasonally. Other people get allergic rhinitis throughout the year because the allergens are non-seasonal.

Those who suffer from allergic rhinitis frequently have other allergic conditions, such as asthma, or allergic conjunctivitis.

Causes

There are many substances in the environment which when inhaled cause allergic rhinitis. They include:

> House dust mites, which are found in mattresses, pillows, beds, and carpets. It is not the dust mites that cause rhinitis, but rather a chemical in their excrement. Dust mites are present all year round.

> Pollen from trees, grass, and weeds.

> Animal fur, hair, and their urine and saliva. Household pets, such as dogs and cats, are common culprits, but some people are affected by horses, rabbits, and rodents, such as guinea pigs and hamsters.

> Cockroaches.

> Allergens in the work environment, such as wood dust, flour dust, or latex.

Aggravating factors

Some people have a genetic predisposition to allergic rhinitis, but it is the exposure to environmental factors that increases the risk of getting the condition and its subsequent severity. The environmental factors can be indoor or outdoor, and occupational.

The indoor factors include tobacco smoke, nitrogen dioxide from gas-fired ovens, and formaldehyde in building materials. The home environment (like carpets) enhances the survival of house dust mites. Outdoor factors include exhaust fumes from motor vehicles, particularly diesel, carbon monoxide, nitric oxide, and ozone.

Occupational pollutants include compounds like isocyanates and hexachloroplanates.

Associated conditions

There is a strong association between allergic rhinitis and asthma. About three quarters of patients with asthma also have allergic rhinitis. Allergic rhinitis frequently worsens asthma.

Sinusitis, which is an infection of the cavities inside the forehead and cheek bone (sinuses), is a common complication of allergic rhinitis. The normally air-filled sinuses are filled with mucous instead, and if it is not drained away, infection from bacteria and viruses can ensue.

The allergen which affects the nose can also affect the sinuses. The usual symptoms are pain in the forehead, face, or teeth, blocked or running nose, greenish or yellowish nasal discharge, coughing, and even fever.

Infections of the middle ear (otitis media) occur because the ear is connected to the nose by the Eustachian tubes, which can get infected. This condition is more common in children who have earache and even fever.

Management

The diagnosis of allergic rhinitis is often straightforward, with its features of swelling and blockage of the airway, congestion, excess mucous production, sneezing, and runny nose. Other symptoms include itchiness and watery eyes.

Sometimes, allergic rhinitis has to be distinguished from a cold or influenza. There is no fever with allergic rhinitis, unlike a cold or influenza. The symptoms of allergic rhinitis last for weeks and even months, but that of a cold or influenza seldom last more than a week. Patients with allergic rhinitis may have itchy eyes and nose but not those with a cold or influenza.

The identification of the allergen is important in managing the condition. If the cause of allergic rhinitis is doubtful, allergy tests are carried out:

> Skin prick test: This involves placing the allergens on the arm and pricking the skin to introduce the allergens into it. If the skin becomes itchy, red, and swollen, it is a positive reaction.

> Blood test: This involves measuring the level of IgE antibody produced in the blood in response to a suspected allergen.

The doctor will prescribe treatment after taking into consideration the type, frequency, and severity of the symptoms, patient’s preference for oral tablets or a nasal spray, and whether there are allergic conditions like conjunctivitis or asthma.

The medicines prescribed include antihistamines and corticosteroids. Antihistamines block the action of the histamine released during an allergic attack. They can be taken as tablets, as nasal sprays, or drops. The earlier antihistamines had drowsiness as a side effect. The newer antihistamines do not usually cause drowsiness, although some people still get this side effect.

Special precautions are necessary if antihistamines are used in children and pregnant women.

Corticosteroids act by affecting the body’s response to the allergen. It takes a longer time to act but lasts longer. The side effects, although rare, include nasal dryness and irritation, and nose bleeds.

It is not advisable to use nasal decongestants for more than a week as they can worsen the congestion. Nasal decongestants cannot be used if one is taking the group of anti-depressants called monoamine oxidase inhibitor (MAOI).

There are occasions when a referral will be made to a specialist, particularly if the response to treatment is unsatisfactory. After an evaluation, the specialist may prescribe different medicines or suggest immunotherapy. This treatment is only suitable for certain types of allergic rhinitis. It involves increasing the patient’s exposure to the allergen gradually so that the patient becomes less sensitive to it, and decreases the likelihood of an adverse reaction when exposed to the allergen in the future.

This treatment has to be done under medical supervision as there is a small risk of an anaphylactic shock, which is potentially life threatening.

Surgery is rarely recommended. However, if there are nasal polyps which worsen the allergic rhinitis, surgery may be beneficial.

Prevention is always better than cure. The avoidance of the allergen will prevent the allergic rhinitis. A discussion with the doctor will be helpful on the prevention of exposure to dust mites, animal flakes, and pollen.

■ Source: Dr Milton Lum