These are things that you get into contact within a variety of ways:
Through the mouth when you eat or drink certain foods, specific ingredients, a food additive, a particular medicine. Through the air when you breathe in. For example pollen, smoke, dust, molds, fumes, sprays, or fur from pets. Through the skin when it touches, rubs or pricks through; something you apply on the skin, a substance in the fabric or jewellery you wear, something that rubs or pricks your skin like a plant or insect. It may be injected into you like medicine or intravenous fluids. An individual could be sensitive to one or a variety of allergens.

If someone you are related to by blood has asthma or the problems related to allergies that are mentioned above.

If you have asthma or allergy symptoms.

If you are a child.

Common allergic disorders include allergic rhinitis or hay fever, asthma, eye allergy, allergic eczema, hives or urticaria, and anaphylactic shock is at the life threatening end of the spectrum.

One can get serious allergic reaction that starts rapidly, causes serious problems and can lead to death. This is anaphylaxis. It can cause an itchy rash, throat or tongue swelling, difficulty in breathing, vomiting, lightheadedness, and low blood pressure. It is most commonly triggered by foods, medications and insect stings.
Some people with allergies also have asthma, a condition of the airways that causes problems like recurrent coughs, wheezing, and shortness of breath. Exposure to allergens can trigger an asthma attack. Severe attacks of asthma can be life threatening.
People with respiratory allergies and at an increased risk of developing irritation or infection in the sinuses, the ears, the throat and the lungs.

When you come into contact with an “allergen” your body detects it and makes proteins called antibodies against it. The antibody latches onto the allergen or antigen and instructs the body to release certain chemicals to facilitate the removal or destruction of the offender. It is these chemical that cause allergy symptoms.

Sometimes you already know what you are reacting to; other times you may be mistaken; many times you just have no idea what it is. It is important to work with your doctor to find out the specific allergy and design efficient treatment strategy. Typically the doctor will ask you questions to understand you ,your problem , your environment and whether your family members have allergy related problems. A physical exam will help reveal if you have features of past or current allergic reactions. Various tests may also be needed.

The most helpful test in finding the cause of allergies are skin tests. There are different ways of doing them but all involve exposing the skin to small amounts of extracts from common allergy-causing substances and observing changes on the skin over time. The test may involve a scratch test or prick test where the allergen is scratched onto the upper layer of the skin. The doctor could inject a small amount of the allergen just under your skin-an intradermal test. He could also stick a patch containing the allergen onto an area of your skin-a patch test. The substances may cause you to see a rash or swelling or redness that may be accompanied by an itchy, stinging, or burning sensation. That is how the doctor knows what may be causing your problem.
There are allergy blood tests that detect the presence of and measure the amount of antibodies formed against specific allergens. These include Enzyme-linked immunosorbent assay (ELISA, or EIA) and Radioallergosorbent test (RAST). These may be ordered under some circumstances for example if you tend to get very severe reactions , if your skin has a problem that makes skin tests difficult or if you must continue taking medication that interferes with the test results.

Treatment of allergy takes into account one’s medical history, the results of allergy tests and how severe one’s symptoms are. Three strategies may be employed:

Avoiding allergens where possible.

Taking medications to suppress the allergy symptoms. There are many safe prescription and over-the-counter anti-allergy medicines. There are some for applying on affected skin, others are eye drops, nose drops or nasal sprays; some may be swallowed in syrup or tablet form; In hospital there are even injectable ones. They also work in a variety of ways. Talk to your allergy team on what would be appropriate to treat your problem.

Immunotherapy where the allergens are administered to the body either by injections or put under the tongue starting with small doses and increased over time. With time the person becomes progressively less sensitive to the allergen. Allergy shots may work well for certain allergies.

Talk to your allergist about the risks and benefits of these approaches.