What is an allergy?
An allergy is when the body reacts to a substance that is usually harmless, an example being pollen. The substance that triggers the reaction is known as an allergen.
The most common allergens are:
- Pollen from trees and grasses
- Proteins secreted by house dust mite
- Foods such as peanuts, milk, and eggs
- Pets such as cats and dogs, and other furry or hairy animals such as horses
- Insects like wasps and bees
The body produces antibodies to attack anything that it sees as a threat. In people who suffer with allergies their body produces antibodies against the allergen, such as pollen. This is a specific type of antibody called IgE. When that person comes into contact with the allergen, their body produces IgE, which in turn causes a particular type of cell, called mast cells, to release histamine. It is the release of histamine that causes the symptoms of allergies and hence why taking antihistamines can settle the reaction.
Mast cells are found in the skin, nose, eyes and mouth, throat, stomach and gut, which explains why the common symptoms of allergies are:
- Runny nose
- Nettle rash / hives
- Itchy eyes, ears, lips throat & palate (roof of mouth)
- Shortness of breath
- Sickness, vomiting, & diarrhea
The most important part of diagnosing an allergy is taking a thorough history. Often the cause is obvious and no tests are required. Keeping a record of your symptoms may also help to work out what is the allergen.
- Do they occur at any particular time of the day?
- Do you only get symptoms at certain times of the year?
- Do you suffer more at night time or during the day?
- Are your symptoms linked to a particular place, i.e. home or work environment?
- Do your symptoms occur when you are in the house as well as outside?
- Does exposure to animals bring on your symptoms?
- Do you think that any food or drink brings on your symptoms?
However, sometimes tests can be helpful particularly if the reaction is more severe, or the cause it is not immediately apparent.
Skin Prick Testing
Skin prick testing is usually the first test recommended when an allergy is suspected. These tests can be carried out on all age groups, including babies. It is simple and quick with results taking about 15-20 minutes.
The skin prick test introduces a tiny amount of allergen into the skin. It is usually carried out on the forearm, but if the patient has bad eczema the test can be performed on the back. A drop of the allergen solution is placed on the arm and the skin is then pricked through it. It is not particularly painful, but can be a bit itchy.
It is important that anyone having this test must stop antihistamines or other allergy medications they are taking 1 week prior to the test.
If the test is positive, the skin becomes itchy and red, with a central wheal. The appearance is similar to a nettle sting.
A negative response to skin prick testing usually indicates that you are not sensitive to that allergen.
ImmunoCap® is a blood test that can measure the amount of IgE antibodies to over 100 different allergens.
This can be useful if the exact cause of the allergy is unclear, or there are practical reasons why skin prick testing would not be possible such as extensive eczema.
The sample is sent off for analysis and a full report confirming or excluding IgE antibodies to the allergens will be sent to you.
Lactose intolerance tests
This is often undertaken on patients with symptoms of irritable bowel syndrome.
This is a series of breath tests that are undertaken over a period of 3 hours and it is essential that you are fasted prior to the examination.
The results are available at the end of the test and skin prick tests for milk, wheat, oat and egg are undertaken at the same time.
Arranging for allergy tests
Dr Palmeri is trained in allergy medicine and undertakes the tests.
We advise that you discuss with your normal doctor whether you need allergy testing. It may be that your doctor will be able to ascertain the cause of your problem and no further tests are required.
If it is felt allergy testing should be undertaken, your doctor will arrange an appointment for you to attend the allergy clinic where Dr Palmeri will decide what tests would be most appropriate for you.