Allergies: An Overview

Allergies are the negative reactions bodies have to particular foods or substances. They are very common, affecting as many as one in four people in the UK at some point in their lives according to the NHS.

Everyone responds to reactions differently, with symptoms ranging from mild to severe. The causes of allergies are fairly consistent between people, however, with dust, grass, pollen and certain foods being frequently reported as allergens.

Allergies are particularly common in children, and although some allergies disappear as a child gets older, most allergies are lifelong affairs – with some adults developing all new allergies along the way too.

Frustrating though some allergies may be to accommodate, allergic reactions are generally easily avoided with enough communication between the allergy sufferer and friends, family and co-workers. Further allergic reactions are usually mild – though obviously exceptions do exist and severe reactions can undoubtedly occur.

What causes an allergic reaction?

Allergic reactions occur when the immune system treats a substance as harmful, producing antibodies that target the non-harmful allergen. This reaction can inflame the skin, sinuses, airways or digestive system to varying degrees – producing minor rashes and irritation to some, fully fledged anaphylaxis to others. The latter is a life-threatening emergency, the former is not.

What are the most common allergies?

The most common allergens, according to the NHS, are as follows:

• Grass and tree pollen (hay fever)
• Dust mites
• Animal dander (skin or hair)
• Nuts, fruit, shellfish, eggs and cows' milk
• Insect bites and stings
• Ibuprofen, aspirin and certain antibiotics
• Latex
• Mould
• Household chemicals

Research has not made it clear why allergies develop in people. All we know right now is that most people affected by allergies have a family history of allergies or conditions like asthma or eczema.

Research is even less clear as to why the number of reported allergies is increasing year on year. The prevailing theory (sometimes referred to as the 'hygiene hypothesis') is that because we are living in cleaner environments than we have in the past, and have the tools at our disposal to keep them that way, we are less frequently exposed to infections and microorganisms.

The infections that we are protecting ourselves from with extreme cleanliness are usually instrumental in promoting the normal development of immune responses. When exposure to them is reduced, without also reducing exposure to otherwise harmless environmental allergens, there is a tendency for people to develop inappropriate immune responses to common, typically harmless environmental allergens – and so an allergy is born.

The symptoms you may or may not observe depend on the substance that triggered them. As such, there are different groups of common signs to look out for depending on the allergen:

An allergic reaction to pollen might cause:

• Sneezing
• Itchy eyes, nose or roof of mouth
• A stuffed or runny nose
• Watery, red or swollen eyes

An allergic reaction to food might cause:

• Swelling of the lips, tongue, face or throat
• Tingling in the mouth
• Hives
• Anaphylaxis

An allergic reaction to an insect sting or bite might cause:

• Swelling at the site of the sting
• Itching or hives throughout the body
• Coughing, chest tightness or shortness of breath
• Anaphylaxis

An allergic reaction to a specific medicine might cause:

• Facial swelling
• Itching or hives throughout the body
• Coughing, chest tightness or shortness of breath
• Anaphylaxis

An allergy is an immune response to a traditionally harmless substance. An intolerance produces unpleasant symptoms, for example diarrhoea, but does not involve the immune system.

Both allergies and intolerances are differentiated from sensitivities, which provoke exaggerated, but not extreme effects to a substance. A caffeine sensitivity, for example, might produce trembling or heart palpitations.