Rhinitis

Allergic rhinitis is caused by an allergic reaction to an allergen, such as pollen, dust and certain animals. It can result because of an oversensitive immune system.
In cases of allergic rhinitis, the immune system reacts to an allergen as if it were harmful. The immune system is the body’s natural defence against infection and illness.
If your immune system is oversensitive, it will react to allergens by producing antibodies to fight them off. Antibodies are special proteins in the blood that are usually produced to fight viruses and infections.
Allergic reactions do not occur the first time you come into contact with an allergen. The immune system has to recognise and ‘memorise’ it before producing antibodies to fight it. This process is known as sensitisation.
After you develop sensitivity to an allergen, whenever it comes into contact with the inside of your nose and throat, it will be detected by antibodies called immunoglobulin E (IgE).
These cause cells to release a number of chemicals (including histamine), which cause the symptoms of allergic rhinitis, such as:

• swelling of the mucus membrane (the inside layer of your nose) – which blocks the airway and causes congestion

• production of excess mucus – which occurs as a result of the swelling and causes sneezing and a runny nose

There are a number of common allergens which can trigger allergic rhinitis – breathing in tiny particles of these allergens is enough to set it off. The most common airborne allergens that cause rhinitis are described below.

House Dust Mites:
House dust mites are tiny insects that feed on the dead flakes of human skin. They can be found in mattresses, carpets, soft furniture, pillows and beds.
Rhinitis is not caused by the dust mites themselves, but by a chemical found in their excrement. Dust mites are present all year round, although their numbers tend to peak during the winter.

Tree and Grass Pollen:
Tiny particles of pollen produced by trees and grasses can sometimes cause allergic rhinitis.
Most trees pollinate between early to mid spring. Grasses pollinate at the end of spring and beginning of summer.

Animals:
Many people are allergic to animals, such as cats and dogs.
It is not animal fur that causes the allergic reaction, rather flakes of dead animal skin and their urine and saliva.
Dogs and cats are the most common culprits, although some people are affected by horses, cattle, rabbits and rodents, such as guinea pigs and hamsters.

Work-Related Allergens:
Some people are affected by allergens found in their work environment, such as wood dust, flour dust or latex.

At Risk Groups:
It is not fully understood why some people become oversensitive to allergens. However, some people are more likely to develop an allergy because it runs in their family.
If this is the case, you are said to be atopic or to have atopy. People who are atopic are more likely to develop allergies because they produce more IgE antibodies than other people.
Environmental factors also seem to play a part. Studies have shown certain things may increase the chance of a child developing allergies. These include:
• growing up in a house where people smoke
• exposure to dust mites
• exposure to pets
• using antibiotics
Non-allergic rhinitis occurs when the nasal lining becomes swollen and inflamed, usually due to both swollen blood vessels and an accumulation of fluid in the tissues of the nose.
Blood vessels inside your nose help to control the flow of mucus by expanding and narrowing. Swelling of the nasal lining causes congestion and stimulates the mucus glands in the nose, resulting in the typical symptoms of nasal obstruction, catarrh (a build-up of fluid in the nasal cavities) and a runny nose.

There are several possible causes of non-allergic rhinitis including:

Viral Rhinitis:
In cases of viral rhinitis, a virus attacks the lining of the nose and throat, resulting in it becoming inflamed and triggering the production of mucus.

Vasomotor Rhinitis:
For reasons that are unknown, people with vasomotor rhinitis have very sensitive nasal blood vessels. Environmental triggers can make the blood vessels expand, leading to congestion and a build-up of mucus. Common triggers include:
• chemical irritants, such as smoke, perfume or paint fumes
• changes in the weather, such as a drop in temperature
• alcohol
• spicy food
• stress

Atrophic Rhinitis:
Inside your nose, there are three ridges of bone covered by a layer of tissue. These layers of tissue are called turbinates. Atrophic rhinitis can occur if the turbinates become damaged.
Turbinates can be damaged by infection, although this is rare in the UK. Bacteria usually responsible for atrophic rhinitis, known as Klebsiella ozenae, are mainly found in India, China and Egypt.
Turbinates play an important role in the functioning of your nose by:
• keeping the inside of your nose moist
• protecting the body from being infected with bacteria
• regulating the air pressure of oxygen you breathe in
• containing important nerve endings that are used to transmit information, such as smells, to your brain
If a certain amount of turbinates are damaged or removed, the remaining tissue will become dry, crusty and prone to infection.
If you have atrophic rhinitis, you may also experience shortness of breath, because the turbinates are no longer able to regulate air pressure effectively and your lungs have to work harder to receive air. Many people also lose their sense of smell (anosmia).
The amount of turbinates that can be lost before atrophic rhinitis develops will differ from person to person. Some people lose a large amount of turbinates and never develop the condition, whereas others develop the condition after losing a small number of turbinates.

Rhinitis Medicamentosa:
Rhinitis medicamentosa is caused by the overuse of nasal decongestant sprays. It can also occur as a complication of cocaine misuse.
Nasal decongestants work by reducing the swelling of the blood vessels in your nose. However, if decongestant sprays are used for longer than five to seven days at a time, they can cause the lining of your nose to swell up again, even after the cold or allergy that originally caused the problem has passed.
If you use more decongestants in an attempt to reduce the swelling, it is likely to make the problem worse. This is sometimes known as ‘rebound congestion’.
It is possible to get locked into a cycle of overuse and dependence on nasal decongestants, in a similar way to becoming addicted to drugs.

Hormonal Imbalance:
Non-allergic rhinitis can also be caused by hormonal changes due to pregnancy, puberty or taking hormone replacement therapy (HRT) or the contraceptive pill. An underactive thyroid gland (hypothyroidism) is another possible cause.
It is thought that hormones play a role in the enlargement of the nasal blood vessels that can lead to rhinitis.