What causes allergic reactions?
Ironically, the incidence of allergies is thought to be increasing as a result of the healthier lifestyle we now have compared with that of our predecessors. Because many harmful viruses and bacteria have been eradicated or neutralized (via vaccines, for instance) it is thought that our immune systems are reacting increasingly to other foreign substances. The tendency to develop an allergy can be inherited and people who are allergic to one substance are likely to have multiple allergies. For example, children with asthma have a greater tendency to suffer from eczema than those who do not have asthma. Allergies may also be related in part to the environment. For example, the pollen count in one country may be higher than another, resulting in higher levels of hay fever in that country.
What tests confirm an allergy?
There are various tests that may be used to establish the cause of allergies, including skin patch testing and skin prick testing. Skin patch testing can be used to test for skin allergies such as hives or dermatitis. Small discs impregnated with various allergens are applied to the back or upper arm and left in place for 48 hours. The skin will be checked for any redness or swelling immediately after removing the patch and also after 48 hours. If there is a reaction, the allergen responsible can be identified from the patch that caused it.
Skin-prick testing involves placing a small amount of different allergen solutions on the skin. The skin is then pricked to allow the solutions to enter under the skin. If there is an allergic reaction to that substance, an itchy welt will appear soon afterward. A number of allergens will usually be tested at the same time. The test is usually done on the forearm but sometimes on the back in infants. Once the allergen is known, the sufferer can minimize exposure to it where possible.
Testing for food allergies can be a long process and usually requires exclusion of certain foods or restricted diets and adding them back to a diet gradually to see when or if symptoms occur. Patients need to be monitored carefully by a doctor or dietitian. However, because the reaction times to various foods can vary from a few hours to days, it may be difficult to identify the cause of the allergic reaction.
Tests for asthma include the use of a peak flow meter and a spirometer to record lung function. These may be particularly useful if a person has an allergy to a substance at work, such as grain or flour or high levels of dust. The asthma may not be present while at a doctor’s office but, if present while at work, it may indicate an allergy to a particular substance in the workplace.