What is Allergy?
The term allergy is used to describe a response to a substance, which is not necessarily harmful in itself, but results in a response and a reaction that causes symptoms and disease, which in turn can cause inconvenience, or a great deal of misery.

An allergy is everything from a runny nose, itchy eyes and palate to skin rash. It aggravates the sense of smell, sight, tastes and touch causing irritation, extreme disability and sometimes fatality. It occurs when the body's immune system overreacts to normally harmless substances.

Allergy is widespread and affects approximately one in four of the population in the UK at some time in their lives. Each year the numbers are increasing by 5ith as many as half of all those affected being children.

What causes an Allergy ?
Allergic reactions are caused by substances in the environment known as allergens. Almost anything can be an allergen for someone. The most common allergens are:

Pollen from trees and grasses, house dust mite, moulds, pets such as cats and dogs, insects like wasps and bees, industrial and household chemicals, medicines, and foods such as milk and eggs.

Less common allergens include nuts, fruit and latex.

An allergic person's immune system believes allergens to be damaging and so produces a special type of antibody (IgE) to attack the invading material. This leads other blood cells to release further chemicals (including histamine) which together cause the symptoms of an allergic reaction.

The most common symptoms are:
Sneezing , runny nose, itchy eyes and ears, severe wheezing, coughing, shortness of breath, sinus problems, a sore palate and nettle-like rash.

It should be understood that all the symptoms mentioned can be caused by factors other than allergy. Indeed some of the conditions are diseases in themselves.

When asthma, eczema, headaches, lethargy, loss of concentration and sensitivity to everyday foods such as cheese, fish and fruit are taken into account, the full scale of allergy be appreciated.

What is an Allergen?
The substance that causes an allergic response is known as an allergen. Allergens contain protein, and almost anything can be an allergen for someone.

The most common are house dust mites, pollen from trees and grasses, cats, dogs, insects such as wasps and bees, milk, eggs and peanuts.

Less common allergens include tree nuts, fruit and latex.

Protein is often regarded as just something that we eat. It is, in fact, an organic compound containing hydrogen, oxygen and nitrogen, which form an important part of living organisms. There are, however, some non-protein allergens which include penicillin and some other drugs. For these to cause an allergic response they need to be bound to a protein once they are in the body.

A person's immune system believes that the invading allergens are damaging and in response the body produces an antibody ("IgE") to attack them. This in turn leads other cells (i.e. mast cells) to release further chemicals which together cause irritation, inflammation and the symptoms of an allergic response. Some of the conditions or diseases themselves have already been listed, but it should be understood that all the mentioned diseases can be caused by factors other than allergy.

Here are some of the most common symptoms associated with the conditions:

• Sneezing

• Wheezing

• Sinus pain

• Runny nose

• Coughing

• Nettle rash / hives

• Swelling

• Itchy eyes, ears, lips throat & palate (roof of mouth)

• Shortness of breath

• Sickness, vomiting, & diarrhoea

• Increase in secretions

Allergy is a local or systemic inflammatory response to allergens. Local symptoms are:

• Nose: swelling of the nasal mucosa (allergic rhinitis)

• Eyes: redness and itching of the conjunctiva (allergic conjunctivitis)

• Airways: bronchoconstriction, wheezing and dyspnoea, sometimes outright attacks of asthma. In severe cases the airway constricts due to swelling known as anaphylaxis.

• Ears: feeling of fullness, possibly pain, and impaired hearing due to the lack of eustachian tube drainage.

• Skin: various rashes, such as eczema, hives (urticaria) and contact dermatitis.

• Head: while not as common, headaches are seen in some with environmental or chemical allergies.

Systemic allergic response is also called anaphylaxis; multiple systems can be affected including the digestive system, the respiratory system, and the circulatory system. Depending on the rate of severity, it can cause cutaneous reactions, bronchoconstriction, edema, hypotension, coma and even death. This type of reaction can be triggered suddenly, or the onset can be delayed. The severity of this type of allergic response often requires injections of epinephrine, through a device known as the Epi-Pen auto-injector. The nature of anaphylaxis is such that the reaction can seemingly be subsiding, but may recur throughout a prolonged period of time.

Hay fever is one example of an exceedingly common minor allergy - large percentages of the population suffer from hayfever symptoms in response to airborne pollen. Asthmatics are often allergic to dust mites. Apart from ambient allergens, allergic reactions can result from foods, insect stings and reactions to medications.