What causes allergies?

Dear Mirror Doctor, Please why do some people have allergies and what causes these allergic reactions?
Thanks
Mohammed.

Dear Mohammed, Allergies or known medically as atopy is a genetically inherited tendency to react to some substances. The allergy is usually mediated by a type of immunoglobin called IgE.

Atopy, a Greek word meaning “special” or “unusual” is a disease characterised by a tendency to “overreact to things”. It may manifest in different parts of the body with the part of the body involved determining its name.

 If it affects the skin - atopic dermatitis, allergic conjunctivitis – eye manifestation, allergic rhinitis – constant running nose and in extreme form, asthma.

With regards to the causes, one study emphasized strong genetic underpinnings of allergies. Environmental factors are also known to play a major role and the 'hygiene hypothesis' is one of the best paradigms available to date to explain the steep rise observed in atopic diseases.

This theory attributes the excess 'cleanliness' of our environments to the decline in the number of infectious stimuli necessary for the proper development of our immune system.

Many studies also suggest that the maternal diet during pregnancy can be a causal factor of atopic diseases (as well as asthma) in offspring. It concluded that consumption of food rich in antioxidants and certain lipids is preventive.

Most patients with atopic conditions have atopic eczema or atopic dermatitis usually from infancy. Atopic eczema is an extremely itchy skin condition with a hallmark rash that appears most often over the flexural regions (e.g., back of knees, crook of elbows) but can involve almost every region of the body.

Crusty, scaly, flattened, reddened or darkened lesions of atopic eczema can appear almost everywhere, but are worse in certain areas or after exposure to certain irritants or allergens (e.g., washing hands with a perfumed or otherwise allergenic soap, wearing a wool or scratchy sweater or skirt, rolling across freshly cut lawns).

The single most important feature associated with atopic eczema lesions is that they are extremely itchy, and the itch can occur even before the lesions erupt on the skin and are visible.

Patients with atopic eczema usually develop what is referred to as the “allergic triad” of symptoms i.e., eczema, hay fever, and asthma. They also have a tendency to have food allergies, and other symptoms characterized by their hyper allergic state.

There are certain environmental factors that contribute to its appearance in infants and children, but the underlying cause is a genetic tendency to be hyper allergic.

Atopic eczema cannot be prevented in infants because of its genetic origins however, as the children grow, they learn to avoid whatever the precipitants are.

Atopic syndrome can be fatal for those who experience serious allergic reactions, such as anaphylaxis, brought on by reactions to food or environment.

Allergic rhinitis is a collection of symptoms, mostly in the nose and eyes, which occur when you breathe in or come into contact with something you are allergic to, such as dust, dander, or pollen.

This type of allergic rhinitis is commonly called hay fever. When a person with allergic rhinitis breathes in an allergen such as pollen or dust, the body releases chemicals, including histamine as a mediator in the allergy symptoms such as itching, swelling, and mucus production commonly referred to as the running nose.

The amount of pollen in the air can play a role in whether hay fever symptoms develop or not. Hot, dry, windy days are more likely to have increased amounts of pollen in the air than cool, damp, rainy days when most pollen is washed to the ground.

Symptoms that occur shortly after coming into contact with the substance you are allergic to may include:
•  Itchy nose, mouth, eyes, throat, skin, or any area
•  Problems with smell
•  Runny nose
•  Sneezing
•  Tearing eyes
Symptoms that may develop later include:
•  Stuffy nose (nasal congestion)
•  Coughing
•  Clogged ears and decreased sense of smell
•  Sore throat
•  Dark circles under the eyes
•  Puffiness under the eyes
•  Fatigue and irritability
•  Headache
•  Memory problems and slowed thinking

Another form of atopy is allergic conjunctivitis which is "an immunologic reaction of the conjunctiva (whitish part of the eye) associated with itching, redness, and tearing; it is typically seasonal, is brought about by allergy (rather than infection), may be associated with other stigmata of allergic reactions, and may affect up to 10% of the population."

The following allergens are commonly found to cause allergic conjunctivitis:
•  Pollen
•  Animal fur
•  Eye drops
•  Make-up
•  Dust mites

The best treatment, as has been stated earlier is to avoid what causes the allergic symptoms in the first place.  It may be impossible to completely avoid all the triggers, but one can often take steps to reduce exposure.
Prevention is by avoiding the triggers, something that could be very daunting identifying in the child but very easy to identify in the adults.
All you need to do is to stay away from them, especially those vegetables and fruits that you react to.

astom2@yahoo.com
A member of Paediatric Society of Ghana