Causes of Allergy – Allergy Reactions Follow Repeated Exposure
An allergic reaction is brought on by exposure to specific foreign substances, or allergens, mostly proteins, or small molecules attached to proteins — that sensitize the body’s immune system so that it reacts to normally harmless substances as though they were dangerous intruders.
Contrary to popular misconception, allergy attacks don’t usually begin out of the blue.
The causes of allergy generally takes a period of “sensitization” through one or more exposures to a specific trigger (or triggers) to build up an allergic response. When someone first wears latex gloves, for instance, or when a cat first joins a household, there is usually no reaction, but repeated contact may eventually cause a latex rash or a cat-induced runny nose and itchy eyes. ( Further pet allergy info )
Once someone is sensitized, it may take only take tiny amounts of the allergen – traces of cat dander or latex to trigger symptoms, sometimes severe ones.
Occasionally someone appears to have an allergic reaction on first encountering a food or other allergen, but there must there must been unknown exposure on some past occasion.
Sometimes it takes long-term exposure to what causes allergy symptoms — months to a year or more — to build up an allergy, for instance to certain pollens, as in hay fever.
Considering the vast number of foreign substances we encounter each day, it’s surprising how few substances are the cause of allergy.
For example, of all the foods eaten, only a few commonly cause allergies.
This is the list of the most common food allergy causes in North America.
- Cow’s milk,
- Legumes (such as peanuts and soy)
- Tree nuts.
Similarly, of all the different types of pollen that fly about in North America, hay fever is commonly caused by those from only a few grasses, weed and tree species. (Further Seasonal Allergy info here)
Depending on their entry route, allergens cause different symptoms. Inhaled allergens such as pollen and moulds typically cause nasal and lung symptoms; those eaten (ingested) may produce tongue tingling, gastric upsets and swollen breathing passages. Ingested and injected allergens tend to induce the most severe, body-wide reactions.
The extent and severity of an allergic response range from the merely annoying to the life-endangering.
For example, the stuffy nose and runny eyes of hay fever, and the contact rash that develops from some cosmetics, are distressing but not life- threatening, although they can lead to complications, especially if left untreated.
In contrast, a food allergy or bee sting that jeopardizes breathing or affects the heart and circulation can culminate in allergic shock, and even in the death of an otherwise healthy person.
Anaphylaxis, the most severe allergic reaction, affects several body systems at once and can occur within minutes.
Its possible warning signs include widespread hives, flushing, a sudden drop in blood pressure and difficulty breathing. It can be rapidly fatal if not immediately treated.