What Is an Allergy? Types of Allergies, Allergy Tests, and Diagnosis

Allergies are common and can affect people of all ages. Some people develop mild symptoms such as sneezing, itching or a skin rash, while others may have more serious reactions. Understanding the type of allergy involved and the right type of allergy test can help a doctor identify the possible trigger and plan suitable care.

An allergy happens when the immune system reacts to a substance that is usually harmless to most people. This substance is called an allergen. Common allergens include dust mites, pollen, pet dander, certain foods, medicines, insect stings and substances that touch the skin.

What Is an Allergy?

The immune system normally protects the body from harmful germs. In an allergic reaction, it mistakenly treats a harmless substance as a threat and releases chemicals such as histamine. This can cause symptoms in the nose, eyes, skin, lungs or digestive system.

A person may be sensitive to one allergen or several allergens. The same allergen may also cause different symptoms in different people.

Common Symptoms of an Allergy

Symptoms depend on the allergen and the part of the body affected. Common signs include:

• Sneezing, runny nose or blocked nose
• Itchy, red or watery eyes
• Skin itching, redness, hives or rash
• Swelling of the lips, face or eyes
• Coughing, wheezing or breathlessness
• Stomach pain, nausea, vomiting or diarrhoea after certain foods

A severe allergic reaction called anaphylaxis can cause breathing difficulty, throat or tongue swelling, dizziness or fainting. It is a medical emergency and requires immediate treatment.

What Are the Different Types of Allergies?

There is more than one allergy type. Allergies are often grouped according to the trigger or the part of the body affected.

1. Respiratory Allergies

Respiratory allergies may be triggered by pollen, dust mites, mould or pet dander. They can cause sneezing, nasal congestion, itchy eyes, coughing or wheezing.

If a person has repeated cough, wheezing or breathlessness, a Pulmonary Function Test (PFT) may also be advised to assess airflow and check for conditions such as asthma.

2. Skin Allergies

There are different types of skin allergy, and they do not always look the same.

Allergic contact dermatitis may develop after contact with substances such as nickel, fragrances, cosmetics, hair dyes or chemicals. Hives, also called urticaria, appear as raised, itchy welts and may be linked to foods, medicines, infections or other triggers.

Eczema can cause dry, itchy and inflamed skin. Allergy may contribute in some people, but eczema is not always caused by an allergy. Because skin conditions can look similar, proper evaluation is important.

3. Food Allergies

A food allergy occurs when the immune system reacts to a particular food protein. Common food allergens include milk, eggs, peanuts, tree nuts, wheat, soy, fish and shellfish.

The type of food allergy and its symptoms can differ between people. Reactions may include hives, swelling, vomiting, stomach discomfort, coughing, wheezing or, in severe cases, anaphylaxis.

Food intolerance is different from a food allergy because it usually does not involve the immune system.

4. Drug Allergies

Some medicines can cause allergic reactions in certain people. Symptoms may include rash, hives, swelling or breathing problems.

A suspected drug allergy should be discussed with a doctor before the medicine is taken again.

5. Insect Sting Allergies

Bee, wasp and other insect stings usually cause pain and swelling at the site. In people with an insect sting allergy, the reaction may become widespread or severe and may need urgent medical care.

What Type of Allergy Test Is Used?

There is no single type of allergy test that suits everyone. The right test depends on the symptoms, suspected trigger, age, medical history and medicines being taken.

Skin Prick Test

A skin prick test is commonly used to check for immediate allergic reactions. Small amounts of suspected allergens are placed on the skin, and the surface is gently pricked. The healthcare professional then checks whether a raised reaction develops.

It may be used when allergies to pollen, dust mites, pet dander or certain foods are suspected.

Allergy Blood Test

A doctor may recommend a blood test that measures allergen-specific immunoglobulin E, also called specific IgE. It can help identify sensitisation to a suspected allergen.

However, a positive result does not automatically prove that the allergen is causing the person's symptoms. The result must be interpreted together with medical history and actual reactions to the suspected allergen.

General blood tests may also support the wider evaluation. For example, a Complete Blood Count (CBC) includes eosinophils, which can sometimes be raised in allergic conditions. However, a CBC cannot identify the exact allergen responsible. VRX's CBC test information also notes that raised eosinophils can be seen with allergic conditions.

Patch Test

Patch testing is mainly used when allergic contact dermatitis is suspected. Possible allergens are placed on patches applied to the skin and checked later for a delayed reaction.

This is different from a skin prick test because it is mainly designed to identify delayed skin reactions.

Oral Food Challenge

For some suspected food allergies, a doctor or allergy specialist may recommend a supervised oral food challenge.

During the test, small amounts of the suspected food are given gradually while the patient is monitored for a reaction. Because an allergic reaction can occur, an oral food challenge should be performed under appropriate medical supervision with facilities to manage a severe reaction if necessary.

How Is an Allergy Diagnosed?

Allergy diagnosis usually starts with a detailed medical history.

A doctor may ask questions such as:

• When do the symptoms occur?
• Do symptoms appear after eating a particular food?
• Are symptoms worse around dust, pets or pollen?
• Does a particular cosmetic or chemical cause a skin reaction?
• Did symptoms start after taking a particular medicine?
• Is there a family history of allergy or asthma?

After reviewing the symptoms, a doctor may choose the most suitable test.

An allergy test result should not be interpreted on its own. A person can sometimes have a positive allergy test without developing symptoms when exposed to that substance. This is why symptoms, medical history, clinical examination and appropriate testing are considered together when making a diagnosis.

When Should Someone Consider Allergy Testing?

A person may be advised to discuss allergy testing with a healthcare professional if they experience:

• Repeated unexplained skin rashes
• Frequent hives
• Recurrent sneezing or nasal congestion
• Persistent itchy or watery eyes
• Coughing or wheezing around possible triggers
• Reactions after eating certain foods
• Unexplained swelling
• Repeated symptoms after exposure to dust, pets or pollen

Testing may also be helpful when symptoms keep returning but the exact trigger is unclear.

Allergy-Related Diagnostic Testing at VRX Diagno Lounge

Proper diagnosis is important because allergy symptoms can sometimes look similar to other health conditions.

VRX Diagno Lounge provides pathology and diagnostic services across Mumbai, including blood investigations and respiratory testing.

A CBC Test may form part of a general medical evaluation and provides information about different blood cells, including eosinophils. However, it should not be treated as a stand-alone test for identifying a specific allergy.

For patients experiencing repeated coughing, wheezing or respiratory symptoms, a Pulmonary Function Test may be recommended by a doctor to assess lung function. VRX's PFT service is available at its diagnostic centres and also notes allergen testing as a follow-up investigation available at the Goregaon West centre.

The exact allergy investigation required should always be selected based on symptoms and medical evaluation rather than choosing a test without clinical guidance.

Conclusion

An allergy is an immune-system reaction to a substance that is normally harmless. There are several allergy types, including respiratory allergies, skin allergies, food allergies, drug allergies and insect sting allergies.

Since different allergies can cause similar symptoms, identifying the correct cause is important. Depending on the suspected allergy, diagnosis may involve a skin prick test, specific IgE blood test, patch test or supervised food challenge.

No single test can provide every answer. A healthcare professional should consider symptoms, medical history, examination and appropriate test results together.

If allergy symptoms are frequent, unexplained or affecting daily life, proper medical evaluation and diagnostic testing can help identify the possible cause and guide the next steps.