Why Allergies occur
Allergies occur when the immune system overreacts to normally harmless substances in the air we breathe and food we eat.
This immunological response sets off a chemical known as histamine, which causes swelling in surrounding tissues and brings on allergy symptoms such as sneezing, a runny nose and watery eyes.
It’s not known why some people develop allergies and others don’t, but common to all allergic individuals is the overproduction of antibodies by the name of immunoglobulin E, which jump to the defence when sensing an ‘invader’, such as a dustmite lodged in the nose.
These antibodies bind to mast cells throughout the body, setting off the release of histamine whenever the invader (or ‘allergen’) comes back again.
Different types of immunoglobulin E (IgE) antibodies target different allergens, so if you’re allergic to many things, such as pollen, dustmites and cat dander, it means your body is producing many types of IgE antibodies.
Common Types of Allergy and Symptoms
Seasonal allergic rhinitis: Otherwise known as ‘hayfever’, this occurs when pollen and mould spores enter the nose and eyes, causing sneezing, a runny nose, headaches and itching of the nose, eyes, roof of the mouth and back of the throat. Airborne substances can also affect the lining of the lungs, causing wheezing or allergic asthma
Perennial allergic rhinitis: This is an allergy to house dust that may contain mould spores, dust mites and pet dander. Perennial allergies usually affect the nose, not the eyes – except when irritants in the form of eyedrops or cosmetics contact the eye causing allergic conjunctivitis
Food allergy: Certain foods can be absorbed into the bloodstream causing hives, nausea, diarrhoea, itching of the mouth, a runny nose or asthma. In severe cases, food allergy can cause a severe anaphylactic reaction where tissues swell, the airway becomes congested and blood pressure drops
Anaphylaxis: In a small number of people allergens can trigger a life-threatening response. An anaphylactic reaction is a systemic, whole-body reaction that can make breathing difficult, cause blood pressure to fall, and lead to collapse
Eczema (atopic dermatitis): Eczema often affects atopic individuals who may also suffer from allergic rhinitis and/or asthma. It can be triggered by heat, low humidity and emotional stress, resulting in a red, itchy rash that sometimes develops into oozing pustules. Eczema can appear on the face, both hands, both feet, insides of elbows or backs of knees
Contact dermatis: In contact with skin, some allergens (such as latex gloves, antibiotics, nickel or preservatives) and irritants (such as solvents, soaps, detergents and even water) can cause an itchy rash confined to the area of contact, sometimes resulting in swelling and large blisters. Contact dermatitis has a delayed onset, usually developing between 12-48 hours after contact with the offending substance
Urticaria (hives): Hives appear as slightly elevated wheals in a defined area of the body, usually as an allergic response to insect venom, medications or certain foods. But urticaria isn’t always due to an established allergy: though histamine release is always the cause, histamine can be released for reasons other than IgE antibodies binding to mast cells
Allergic angioedema: Usually seen in conjunction with hives, allergic angioedema is a swelling beneath the skin affecting large areas such as the face and throat. It can be caused by anything from food dye through to medication.
Are Allergies Inherited?
Specific allergies are not inherited, but the tendency to be allergic is. If your genetic makeup predisposes you to allergic disease, your allergy is of the ‘atopic’ kind.
Those with many IgE antibodies can have a cluster of allergies, manifested as hayfever, atopic eczema and allergic asthma.
With no family history, a child has a 5-15% chance of developing allergies. But where one parent has allergies, they’ll have s a 25% chance, and where two parents have allergies, a 50-60% chance.
But genes aren’t solely responsible for causing allergy – the environment plays a large role too, which explains why allergies are largely a ‘Westernised’ phenomenon.
According to the ‘hygiene theory’, our clean modern-day environment and increased use of antibiotics has led to immune dysfunction, where in the absence of harmful bacteria to attack, the immune system has turned its guns on harmless environmental substances instead.
Coupled with the fact we’re exposed to more pollution and live in heavily carpeted homes prone to dust and mould build-up, allergies are now part and parcel of life in the developed world.
Prevention and Treatment
Your main goal is to identify the allergen and avoid it in future. Finding suitable symptom relief is also important.
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