Allergies are a very common topic of conversation in our lives – they are so common that they have been described as the ‘epidemic of the 21st century’ and the prevalence of allergies has doubled over the last 20 years.1
The earliest mention of allergies is that of King Menses of Egypt, who was killed by the sting of a wasp at some time between 3640 and 3300 BC. Another report from ancient history is that of Britannicus, the son of the Roman Emperor Claudius. He was allergic to horses and ‘would develop a rash and his eyes swelled to the extent that he could not see where he was going’.1
An allergy is an abnormal reaction of your immune system to a substance, which is called an allergen, which you eat, inhale or touch. Non-allergic people can usually tolerate this substance,2 but if you are allergic to something, your immune system reacts to it as if it were a foreign body and tries to destroy it.3 This is when the body reacts by releasing chemicals like histamine, and these cause the symptoms of the allergy.
Allergy-producing substances are called ‘allergens’ and people who are prone to allergies are called ‘allergic’.4 The most common allergic diseases include allergic rhinitis (hay fever), allergic conjunctivitis (eye allergies) allergic asthma and food allergies.4
A common scene can help explain allergies:4
A few months after the new cat arrives in the house, dad begins to have itchy eyes and episodes of sneezing. One of the three children develops coughing and wheezing. The mom and the other two children experience no reaction at all even though the cat is there. How can this occur? The dad and the one child have become sensitized and have an allergic reaction to the cat while the mom and the other two children are not allergic to the cat and so are not affected.
Parts of the body that are commonly affected by allergies include the eyes, nose, lungs, skin and gastrointestinal tract (stomach).4