What Causes Allergies in Adults? Triggers and Tests

Medically reviewed by Dr. William Aung, DocDocDash’s partner doctor network.
Last reviewed: November 2026.

The Short answer: An allergy happens when your immune system mistakes something harmless, such as pollen, dust mites, a food or a medicine, for a threat and overreacts to it. Allergies can start at any age, including in your 30s, 40s or 50s, and often appear after a move to a new country, a change in hormones or a new environment. The symptoms can look like a cold, a skin rash or a stomach upset, so the trigger is not always obvious. Allergy testing shows exactly what you are reacting to, so you know what to avoid.

What causes allergies?

Allergies are caused by your immune system overreacting to something that is normally harmless. That substance is called an allergen.

It usually happens in two stages:

Sensitisation. The first time you meet the allergen, your immune system wrongly marks it as dangerous and makes antibodies against it, called IgE. You usually notice nothing at this stage.
Reaction. The next time you meet it, those antibodies trigger cells to release histamine and other chemicals. These cause the sneezing, itching, swelling or rash you feel.

Why some people become allergic and others do not depends on a mix of genes and environment. If your parents have allergies, asthma or eczema, you are more likely to develop them too, though not always to the same things.

What are the most common allergy triggers?

Type	Common examples
Airborne	House dust mites, pollen from grasses and trees, mould, pet dander, cockroaches
Food	Shellfish, fish, peanuts, tree nuts, eggs, milk, wheat, soy, sesame
Medicines	Penicillin and other antibiotics, anti-inflammatory painkillers such as ibuprofen
Insect stings	Bees, wasps, ants
Skin contact	Nickel in jewellery, fragrances, hair dye, latex

Why can allergies start in adulthood?

Many people assume allergies begin in childhood, but adult-onset allergies are common. A national US study published in JAMA Network Open found that nearly half of adults with a food allergy developed at least one of them as an adult. Shellfish was the most common food allergy in adults, and it often started in adulthood. The same study found food allergy was more common in women than in men.

Things that can set off a new allergy in adulthood include:

Moving to a new country or city. You meet new pollens, moulds and dust mite levels your immune system has never seen. Many people who move to Australia, Japan or Singapore notice hay fever or itchy eyes for the first time a year or two after arriving.
Hormonal changes during pregnancy or perimenopause.
A new environment, such as a new home, a pet, or a job with exposure to chemicals, flour or latex.
Eating a food more often, or in a new form, than you used to.

Is it an allergy or an intolerance?

The two are often confused. An allergy involves the immune system and can be serious, even from a tiny amount. An intolerance, such as lactose intolerance, affects digestion, causes bloating, gas or diarrhoea, and depends on how much you eat. It is uncomfortable but not dangerous.

The same JAMA Network Open study found that nearly 1 in 5 adults believed they had a food allergy, but their symptoms did not match a true allergy. Testing helps you avoid cutting out foods you do not need to.

What are the symptoms of an allergic reaction?

Symptoms usually start within minutes to 2 hours of contact with the allergen.

Nose and eyes: sneezing, runny or blocked nose, itchy, watery eyes
Skin: hives (raised, itchy welts), redness, eczema flares
Mouth and face: tingling or itchy mouth, swelling of the lips, face or eyes
Stomach: cramps, vomiting or diarrhoea
Chest: coughing, wheezing or tightness

What are the signs of anaphylaxis?

Anaphylaxis is a severe, life-threatening allergic reaction that affects breathing or circulation. Call emergency services immediately if someone has any of these after contact with a possible allergen:

Difficulty breathing or noisy breathing
Swelling of the tongue or throat
Wheezing or a persistent cough
A hoarse voice or difficulty talking
Dizziness, collapse or loss of consciousness
Becoming pale and floppy (in young children)

If the person has an adrenaline auto-injector (such as an EpiPen), use it straight away. Lay them flat, or let them sit if breathing is hard, and do not let them stand or walk.

Which allergy blood test packages are available in Bangkok?

Allergy blood tests measure IgE antibodies to specific allergens from a single blood sample. According to Australasian Society of Clinical Immunology and Allergy (ASCIA), the professional body of allergy specialists in Australia and New Zealand, they are a reliable option when skin prick testing is not easily available, if you have severe eczema, or if you take antihistamines that could affect a skin test. There is no need to stop your allergy medicines, and one blood draw can check dozens of allergens at once.

Several leading hospitals and labs in Bangkok offer allergy blood test packages:

Package	Allergens tested	Price	What is included
Food Allergy Blood Test Package	20 food allergens	5,690 THB	Doctor’s fee and hospital service fee
Inhalation and Environmental Allergy Blood Test Package	20 airborne and environmental allergens	5,690 THB	Doctor’s fee and hospital service fee
Comprehensive Allergy Blood Test Package	36 allergens plus CCD marker	6,490 THB	Doctor’s fee and hospital service fee
Food and Airborne Allergen Screening Program (adults)	40 allergens (20 food, 20 airborne) plus total IgE	11,900 THB	Doctor’s fee and hospital service fee
Allergy Testing (IgE)	102 allergens (50 inhalant, 52 food) plus total IgE and CCD marker	3,150THB	Lab test; results to be reviewed by your doctor

(Prices are as listed by each provider. Prices and allergen lists may change, so check with DocDocDash before booking.)

What do the panels cover?

Food panels typically include egg, cow’s milk, wheat, rice, soy, peanut, tree nuts, sesame, fish and shellfish such as shrimp, crab and lobster, plus meats like pork, beef and chicken. The Thainakarin panel also includes chocolate and glutamate.
Airborne panels typically include house dust mites, cockroach, cat and dog dander, small pets, moulds, grass and tree pollens, and latex. The Thainakarin panel also covers local triggers such as oil palm, acacia and kapok.
The 102-allergen panel adds a wide range of pollens and foods, including Japanese cedar, birch, ragweed and several grasses, plus bee and wasp venom, fruits such as kiwi, peach and mango, and seafood such as squid, oysters, clams and salmon.

Which package is right for me?

Reactions after eating (hives, itchy mouth, swelling, stomach upset): a food allergy panel.
Sneezing, blocked nose, itchy eyes or asthma that comes back often: an inhalation and environmental panel.
Both, or you are not sure: a comprehensive panel that covers food and airborne allergens.
Hay fever that started after moving to Japan, Australia or another country: a wider panel that includes the pollens in your new home, such as Japanese cedar or grass pollens.

If you are unsure, our DocDocDash team can help you choose based on your symptoms.

What is the CCD marker?

CCD stands for cross-reactive carbohydrate determinants. These are sugar structures found in many plants, pollens and insects. They can make a blood test show positive results to several allergens at once, even when you do not actually react to them. Including a CCD marker helps the doctor tell true allergies from these misleading results.

Important to know before testing

A positive result means sensitisation, not always allergy. Your doctor will read the results together with your symptoms. You should not cut foods from your diet based on a test result alone.
Testing works best when you have symptoms. Allergy tests are designed to confirm suspected triggers, not to predict allergies you have never had.

ASCIA warns against unproven tests such as IgG food testing, hair analysis, kinesiology, Vega or electrodermal testing, and online home kits. They can lead to wrong diagnoses and unnecessary, sometimes harmful, diets.

How can I avoid allergic reactions?

Once you know your triggers, avoiding them is the most effective step.

Dust mites: wash bedding weekly in hot water, use mite-proof covers, keep humidity low, and reduce soft toys and carpets in the bedroom.
Pollen: check pollen forecasts, keep windows closed on high-pollen days, and shower after being outdoors.
Food: read ingredient labels every time, ask about ingredients when eating out, and watch for hidden sources such as shrimp paste or fish sauce in many Asian dishes.
Medicines: tell every doctor, dentist and pharmacist about your drug allergies, and consider a medical alert bracelet.
Insect stings: wear shoes outdoors and keep food and drinks covered.

Treatment can also help. Antihistamines and steroid nasal sprays ease everyday symptoms. For allergies to dust mites, pollen or insect venom, allergen immunotherapy (allergy shots or tablets taken under the tongue) can retrain the immune system over 3 to 5 years. If you are at risk of anaphylaxis, your doctor will prescribe an adrenaline auto-injector and an action plan.

Frequently asked questions

What causes allergies? Allergies happen when your immune system overreacts to a harmless substance, such as pollen, dust mites, a food or a medicine, and releases histamine.

Can you develop allergies as an adult? Yes. Nearly half of adults with food allergies developed at least one as an adult. Moving country, hormonal changes and new environments can all play a part.

Which allergy test is most accurate? Skin prick tests and specific IgE blood tests are the most reliable. Your doctor reads the results together with your symptoms to confirm a diagnosis.

Can allergies go away? Some do, especially in children. Adult allergies often last, but treatments such as allergen immunotherapy can reduce symptoms over time.

Are home or online allergy test kits reliable? No. Allergy specialists advise against online kits, IgG food tests and hair analysis, as they are not proven to diagnose allergy.

Book an allergy test with DocDocDash

If you keep sneezing, itching or reacting and do not know why, an allergy test can show you exactly what to avoid. DocDocDash helps you compare trusted partner hospitals in Bangkok and book an allergy consultation and test. Chat with our AI assistant in the DocDocDash app, with doctors on hand to guide you, then compare options and book in one place.