Allergies: How Do You Recognise Them?


Allergies affect up to 20 percent of the world’s population. The severity of allergies varies amongst individuals and can range from a minor reaction to life-threatening complications.  

What is an allergy?

An allergy is the reaction of the immune system to a substance (allergen) in the environment that is usually harmless, such as pollen, food stings and medication. Substances that trigger allergic reactions are known as allergens. 

What causes an allergic reaction?

An allergic reaction occurs when the immune system interprets a foreign substance or allergen as harmful. This leads the development of symptoms following exposure. These allergic reactions can range from mild to severe, with anaphylaxis being the most severe form of an allergic reaction. 

The development of an allergy starts from the pre-sensitization of the allergen. An allergic reaction begins when you inhale, swallow, or touch an allergen. During a reaction, the immune system activates immune cells to produce antibodies that remain on alert for that allergen. 

When you are exposed to the allergen again, these antibodies bind to white blood cells (mast cells) and releases immune chemicals. Histamine is one of these chemicals that causes blood vessels to expand and muscles in the airways to tighten. These chemicals cause inflammatory symptoms of allergic reactions such as rashes, itching and sneezing. 


Symptoms depend on the allergen the body interacts with and can affect namely, the sinuses, mucosal linings, digestive and respiratory tracts. Initial exposures to certain allergens may be mild but can worsen if there is repeated contact with a particular allergen. 

Skin and mucous membranes

  • Atopic dermatitis (Eczema)
  • Urticaria (Hives)
  • Swelling of tissues (Angioedema), especially mouth and face
  • Itching (Pruritus)
  • Contact dermatitis (Rash in contact with an allergen)
  • Oral symptoms – Irritation and swelling of tissues around and inside the mouth 
  • Oral allergy symptoms 

Digestive tract

  • Diarrhoea
  • Constipation
  • Nausea and vomiting
  • Abdominal pain 
  • Indigestion (heartburn) 

Respiratory tract

  • Hay fever – seasonal or perennial rhinitis 
  • Runny nose (Rhinorrhoea) 
  • Allergic conjunctivitis – itchy, watery and reddened eyes
  • Serous otitis media – earache with effusion 
  • Laryngeal oedema – throat tightening due to swelling 


Anaphylaxis is the severe reaction of rapid onset, involving multiple organ systems which results in circulatory collapse and drop in blood pressure. Patients with severe allergies stand at a higher risk of this allergy-induced reaction. This can be triggered by insect stings, medication, and food allergy. In extreme cases, the reaction progresses to anaphylactic shock with cardiovascular disease which can be fatal.

Common symptoms of anaphylaxis are:

  • Light headedness
  • Drop in blood pressure
  • Swelling of the phase and upper torso
  • Severe shortness of breath
  • Nausea and vomiting 
  • Skin rash 

Patients with known anaphylactic risks are usually prescribed with an epinephrine auto-injector (EpiPen) to use during an anaphylactic attack. A second anaphylactic episode may occur even after the first one subsides, and medical attention should still be sought after the first epinephrine shot. 

Other common allergic disorders:


Allergy Testing

  • Cutaneous tests (are routine diagnostic tests in atopic or anaphylactic diseases)
  • Skin prick testing: A single drop of concentrated aqueous allergen extract placed on the skin which is then pricked lightly with a needle point at the centre of the drop. 
  • Intradermal testing: The suspected allergen may be injected just under the skin via an intradermal test. After 20 minutes, the reaction is graded and recorded. This form of testing is similar to a tuberculin test.
  • Skin patch test: A patch containing the suspected allergen can also be placed on the skin for about 48 hours and read 30 minutes after the patch is removed to look for any allergic indications. 

Skin tests are most helpful in diagnosing food allergies, penicillin allergies and allergic contact dermatitis

Blood tests are also used to measure antibody levels against a specific allergen. It is particularly useful when skin testing cannot be done. 


  • Avoid known triggers such as foods and medications which have previously caused an allergic reaction. This includes detailed questioning about ingredients when eating away from home. Ingredient labels should be carefully examined. 
  • Keeping a diary will also help to track what causes or worsens your allergies. 
  • A medical identification tag should be worn by those who know that they have a serious allergic reaction, especially if communication becomes difficult during a reaction. 
  • If history of a serious allergic reaction, one should carry emergency medications. 

Relief from allergies 

  • Antihistamines and decongestants can help to treat certain mild to moderate allergic symptoms. In the case of allergic-type asthma, a doctor may prescribe an inhaler to help to counter these attacks. 
  • Allergy shots: In cases where medication does not alleviate symptoms, allergy shots are administered to stop or reduce allergy attacks. Allergy shots are a form of allergen-specific immunotherapy treatment and are regularly injected over a general period of three months and can go up to five years. This is especially effective for those who suffer from extreme cases of hay fever, allergic asthma and other chronic allergies. However, this mode of therapy may be riskier for those with heart or lung disease.  

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