Allergy Skin Test: Make sure you know what causes your allergies.

Taking an Allergy skin test is a safe and simple way of getting useful information about your allergic conditions.

Doctors have been using skin tests for more than a century in order to diagnose allergies. In this test allergens are put on your skin (mostly your arms or your back) and observed for a sign of an allergic reaction.

These skin tests can, together with your medical history, determine whether symptoms like skin rashes and sneezing are caused by allergies. They can also tell which specific substance triggered the allergic reaction.

All this information helps your doctor to set up a treatment plan. This treatment plan can include avoidance of allergens, medication or immunotheraphy (allergen shots).

Who can benefit from an allergy skin test?

Skin testing is safe for people of all ages, including older adults and small children. It is mainly used to diagnose conditions like eczema, hay fever and allergic asthma.

However, in some cases skin testing is not recommended:

    If you are highly sensitive to a suspected allergen.
You can be so sensitive to the allergen, that even a small amount of it used in the skin test can trigger a severe allergic reaction.

    If you take medications that could interfere with the testing results.
Examples of these are: many sorts of anti-depressants, antihistamines and a few sorts of heartburn medication. Your doctor may decide that it is better for you to keep taking these medicines than to stop using them for a short period in order to prepare for the skin test.

    If you have a severe skin disease.
If large areas of your body are covered with psoriasis or eczema, it can be possible that there is simply not enough clear uninvolved skin to do the testing on.

For those who can't undergo a skin test, the solution is usually a blood test. These tests are done less frequently, even though they can be asaccurate as skin tests. The reason is that they are more expensive. If you are about to start immunotheraphy (This is a series of injections given to you in order to develop an increased tolerance to allergens in your system) you will need either a blood test or a skin test to determine the specific allergens that trigger your allergies.

How to prepare for an allergy skin test?

Before your doctor will recommend a skin test, he will ask detailed questions about your signs and symptoms and your medical history. With your answers, the doctor can determine whether allergies run in your family and if you may also have them.

After this, your doctor will perform a physical examination where he searches for additional clues that can explain the causes of your symptoms.

It is possible that your doctor can get enough information out of your medical history and symptoms to diagnose you and develop a treatment, so that a skin test isn't necessary. But if your doctor isn't completely sure that you have allergies or needs more information about the causes, a skin test may be recommended.

Before undergoing a skin test, your doctor will need a list of all the medications you take. That way he can be sure none of them will interfere with the test results. Some medications can also increase the risk you develop a severe allergic reaction to the test.

How is an allergy skin test performed?

    Puncture or scratch test.
This is the most common of the skin tests. In this test, a very small amount of pure allergen is pricked or scratched into the skin's surface. Allergies to mold, dust mites, insect venom, pollen, pet dander, foods and penicilin are usually detected in this way.

    Intradermal test.
A small amount of pure allergen is injected into your arm. This test is mainly used to detect allergies to insect venom and penicillin.

    Patch test.
A patch with a small amount of allergen is placed on your arm. This test is done to identify the allergens that cause contact irritation. These include fragrances, hair dyes, resins, metals, latex, preservatives and medications.

What to expect during a skin test?

Skin tests cause little to none discomfort. Even when an injection is given, the needle only barely pierces your skins surface. Only mild, momentary irritaion will occur. Some of the test are designed to detect immediate allergic reactions, that occur and are visible within minutes of the allergen's application. Other tests are designed to see if you have delayed allergic reactions, that only show up a few days after the exposure to the allergen.

Tests for immediate allergic reactions.

A puncture or scratch test will look for instant allergic reactions to up to 40 allergens at the same time. Adults will be tested on the forearm, children on the upper back.

The doctor will apply small marks on your skin and apply a small amount of allergen next to each mark. A sharp object is then used to push the allergen into the skin. The allergens are left there for about 15 minutes. The doctor will look for allergic reactions on your skin.

To see if your skin is reacting normal, two substances are put on to double check. Histamine normally causes a skin reaction with everybody, so if your skin is not reacting, the results of the allergen test can't be interpreted. The other one is Saline or Glycerin, they normally cause no reaction to the skin. If your skin is reacting to it, it may mean your skin is over sensitive and the results of the allergen test can't be interpreted either.

tests for delayed allergic reactions. Delayed allergic reactions are conducted via a patch test. Your skin can be exposed to up to 30 allergens at the same time that can cause contact irritations. These patches are worn for 48 hours. During the time you wear them, you should avoid activities that may cause you to sweat heavily and avoid bathing. When you return to your doctor, the patches are removed and the doctor inspects the skin.

Results of test.

You will know the results of a puncture or scratch test before you leave the doctors office. A patch test will take a few days before the results are known. If an allergen produces an allergic reaction, the skin will show a red, itchy bump. It looks a bit like a mosquito bite. The doctor will measure the bump ( the bigger the bump, the more sensitive you are to the allergen). He will then clear your skin with alcohol to remove the allergens remaining in your skin. The doctor will discuss the possible treatment options with you afterwards.

Generally, the skin test is most reliable when diagnosing allergies to airborne substances, such as dust mites, pollens and pet dander.

Risks involved when taking an allergy skin test.

Usually the side effects, if any, are itching and a mildly red skin. This can last for a couple of hours to a day. In rare occasions, the allergens can cause a severe, immediate allergic reaction. It is therefore advised to have a skin test applied at a facility where appropriate emergency equipment and medications are present.