Allergy: Causes, Symptoms and Why Accurate Diagnosis Matters

Adrian Mercer

Allergy may appear to be a common health problem, but it should not always be treated as a minor condition. Some people develop repeated sneezing after exposure to dust or pollen, others develop widespread rashes after eating certain foods, while some may experience breathing difficulty after taking a medicine. In severe cases, a bee or wasp sting can trigger a life-threatening reaction. Because allergic reactions vary widely from person to person, identifying the true cause is the first step toward effective treatment.

An allergy occurs when the immune system reacts excessively to a substance that is usually harmless. Such substances are known as allergens. Common allergens include dust mites, pollen, mould, animal dander, certain foods, medicines, latex and venom from insects such as bees and wasps. The same substance does not affect everyone in the same way. One person may develop a severe reaction to peanuts, while another can eat them without any problem.

Symptoms depend on which part of the body is affected. Nasal allergy can cause repeated sneezing, a runny or blocked nose and itching. Eye allergy may lead to redness, itching and watering. Skin allergy may produce hives, rashes, itching, swelling or eczema. If the respiratory system is involved, the person may develop cough, chest tightness, wheezing or shortness of breath.

Food allergy can cause swelling of the lips, tongue or throat, abdominal pain, vomiting, diarrhoea, hives and breathing difficulty. However, not every problem that occurs after eating a particular food is an allergy. Food intolerance, such as lactose intolerance, is different from a true food allergy. For this reason, symptoms alone should not be used to conclude that a person is allergic to a particular food.

The most dangerous form of allergic reaction is anaphylaxis. This is a rapid and potentially life-threatening condition. The throat may suddenly tighten, the tongue or throat may swell, breathing may become difficult, blood pressure may fall, and the person may become dizzy or lose consciousness. Immediate emergency treatment is essential. Adrenaline is the main life-saving medicine used in anaphylaxis. People with a history of severe allergy should have an emergency plan based on medical advice.

Allergy diagnosis cannot usually be confirmed by a single test. The most important first step is a detailed medical history. Doctors need to know what the person was exposed to, how quickly the symptoms appeared, how long they lasted, whether similar episodes happened before, and whether there is a family history of allergy or asthma. In suspected food allergy, it is particularly useful to know what food was eaten, how much was consumed and how soon the symptoms developed.

Keeping a record of symptoms and possible triggers can also help. A person may note the foods eaten, medicines taken, environmental exposures and symptoms over several weeks. This can help identify a pattern. However, if a substance has previously caused a serious reaction, it should never be deliberately tried again at home for testing purposes.

One of the most commonly used diagnostic methods is the skin prick test. In this test, a very small amount of a suspected allergen is placed on the skin and the surface is gently pricked. If a raised bump or redness appears after a short period, it may indicate sensitivity to that substance. This test is often useful for pollen, dust mites, animal dander and some food allergies.

A positive skin prick test does not always mean that the person has a clinically significant allergy. The immune system may show sensitivity to a substance even when exposure does not cause symptoms in everyday life. For this reason, test results must always be interpreted together with the person’s actual medical history.

A blood test for specific IgE antibodies is another useful method. It may be helpful when skin testing is difficult because of a skin condition, when certain medicines cannot be stopped, or when a skin test is considered unsuitable. However, an elevated specific IgE level alone should not be treated as proof of disease. The result must be assessed in relation to symptoms and exposure.

Patch testing is mainly used to identify allergic contact dermatitis. It is particularly useful for delayed skin reactions caused by substances such as nickel, cosmetics, fragrances, dyes, rubber and other chemicals. Skin prick testing is generally used for immediate allergic reactions, while patch testing is more suitable for delayed contact reactions.

In suspected food allergy, an oral food challenge may sometimes be needed under medical supervision. In this test, the suspected food is given in very small amounts and gradually increased while the patient is carefully observed for a reaction. It is one of the most important methods for confirming or excluding food allergy. Because a severe reaction can occur, it should never be attempted at home. It must be performed in a medical setting where emergency treatment is available.

Medical history is equally important in suspected drug allergy. A past episode of vomiting or headache after taking a medicine should not automatically be labelled as an allergy. An incorrect drug-allergy label may prevent a patient from receiving an effective medicine in the future. At the same time, a true drug allergy can be dangerous if ignored. When necessary, specialists may use targeted skin testing or carefully supervised drug challenges.

If allergy-related asthma is suspected, lung function testing may also be needed. Spirometry can measure how well air moves out of the lungs and can help assess asthma. Nasal allergy, asthma and eczema may occur together, so the overall allergic history of the patient should be considered rather than looking at each symptom in isolation.

Another important issue is avoiding unscientific tests. Various commercial tests are promoted as methods to detect food allergy or “food sensitivity.” In particular, food-specific IgG testing is not considered a reliable method for diagnosing true food allergy. Eliminating large numbers of foods based only on such results can even lead to nutritional deficiencies. Diagnosis should therefore rely on medically accepted methods and professional evaluation.

Once an allergy is confirmed, the main principle of treatment is to avoid the responsible allergen as far as reasonably possible. Antihistamines and nasal steroid medicines can be effective for allergic rhinitis. Appropriate inhalers may be needed for asthma. Skin allergy may require topical treatment along with avoidance of the trigger. In selected respiratory and environmental allergies, immunotherapy may be useful after specialist assessment.

Accurate diagnosis can also reduce unnecessary fear. Many people avoid foods, medicines or environmental exposures for years without confirmation that these substances are actually responsible for their symptoms. This may lead to unnecessary restrictions in diet, lifestyle and treatment. On the other hand, failure to identify a genuine allergy can expose the patient to repeated and potentially severe reactions.

The principle of allergy diagnosis is therefore straightforward: begin with a detailed history, perform an appropriate physical examination and then use targeted scientific testing where necessary. A laboratory report should never be treated as a diagnosis in isolation. Symptoms, timing, exposure history and test findings must be evaluated together before a reliable conclusion is reached.

Allergy is a broad health problem ranging from mild discomfort to life-threatening emergencies. Correct identification of the cause, scientifically validated testing, appropriate treatment and awareness of emergency warning signs can greatly reduce the risk. Recurrent or severe allergic reactions should never be dismissed as trivial. Accurate diagnosis is the first doorway to safe and effective treatment.