• Allergy means ‗altered reaction‘ – it is the inappropriate and harmful response of the body‘s defence mechanisms to substances that are normally harmless.
  • Allergies are caused by the immune system responding inappropriately to harmless substances which can lead to severe illness.
  • Asthma and hay fever are examples of allergic reactions – reacting to allergens that are antigenic but shouldn’t cause harm.
  • When these allergens are inhaled, B cells produce antibodies, including histamines, when the tissues are damaged. and these coat the mast cells that are found in the lining of the airways, sensitizing the body to these allergens
  • Examples of allergens include pollens, dust mite, molds, danders, and certain foods. People prone to allergies are said to be allergic or atopic
  • Now, every time this allergen enters the body, the antibodies are stimulated to release histamine, causing the blood vessels to widen and become leaky – fluid and white blood cells leave capillaries.
  • The area where histamines are released become hot, red and inflamed. Hay fever causes the nose and throat to become inflamed and irritated.
  • It can be an attack of sneezing and runny eyes (hay fever), an itchy red rash (eczema), wheezing when breathing (asthma) or swelling of lips and tongue and vomiting (food allergy). Allergies affect about a third of the population.


Hay fever

  • Hay fever (allergic rhinitis) is the most common of the allergic diseases –        refers to seasonal nasal symptoms that are due to pollens.  
  • Year round or perennial allergic rhinitis is usually due to indoor allergens, such as dust mites or molds.
  • Symptoms result from the inflammation of the tissues that line the inside of the nose (mucus lining or membranes) after allergens are inhaled.
  • Adjacent areas, such as the ears, sinuses, and throat can also be involved. Hay fever is an allergic reaction to airborne allergens.



  • Irritation in the nose resulting in vigorous bouts of sneezing
  • Release of a large volume of watery mucus making the nose run
  • Itchy watery eyes
  • Itchiness in the mouth, throat and ears
  • Blocked nose and sinuses
  • Runny nose
  • Stuffy nose
  • Nasal itching (rubbing)
  • Itchy ears and throat
  • Post nasal drip (throat clearing)




  • Hay fever is not necessarily caused by hay. It generally occurs during the summer months and may be triggered by grass pollen in the air. This generally peaks in June.
  • Tree pollen which peaks in April.
  • Fungal spores such as those of moulds that occur on foliage (including grasses).
  • Non-seasonal hay fever is most often triggered by faecal pellets of dust mites or by hair of pets which may be coated in saliva or urine.



– Treatment of an allergic reaction involves avoiding the allergen as far as possible and preventing or treating the symptoms.




  • Asthma is a breathing problem that results from the inflammation and spasm of the lung’s air passages (bronchial tubes).
  • Asthma is a chronic inflammatory disease of the airways, trigger by a range of allergen.
  • The inflammation causes a narrowing of the air passages, which limits the flow of air into and out of the lungs.
  • Asthma is most often, but not always, related to allergies.
  • When an allergen is inhaled histamine is released by the mast cells in the lungs.
  • This causes inflammation of the lining of small air tubes, secretion of excess mucus and contraction of the muscles in the wall of the airways making breathing difficult if not impossible.
  • Asthmatics have a more serious problem
  • their airways are nearly always inflamed, but during an asthmatic attack this inflammation worsens.
  • Fluid leaks from the blood into the airways and the goblet cells secrete large amounts of mucus, blocking the smaller airways with fluid.
  • This forces the muscles to contract, narrowing the airways and increasing air flow resistance.
  • This makes breathing very difficult and can have fatal consequences.
  • Asthma has been linked to increased air pollution and passive smoking.



The allergens that commonly cause asthma are:

  • House dust mites: These are very small (0.3 mm) and there may be thousands of them of them in a gram of dust in a mattress or carpet. The allergen causing asthma is actually the faecal pellets of the dust mites which are so small they are easily inhaled into the lungs.
  • Pets: the allergen is the saliva or urine on hairs or feathers which are shed around the house.
  • Engine emissions, especially particles of soot: emissions from petrol and diesel engines have been blamed for the increase in childhood asthma but this has not been proven.
  • Organic solvents.
  • Wood and floor dust.
  • Spores from fungi in rotting vegetation.
  • Some medicines.



  • Difficulty with breathing (shortness of breath)
  • Chest tightness; a cough, especially at night.
  • Wheezing – a whistling sound due to air moving through swollen and partially obstructed airways

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