12.JUL.2017 10 MIN READ | 10 MIN READ

Allergies are at best annoying, and at worst life-threatening.

Be it a rash or the sniffles, here’s how to identify an allergy when you have one, and what to do when an allergy acts up.

What is an allergic reaction?

According to Dr Chew Huck Chin, respiratory medicine specialist at Mount Elizabeth Novena Hospital, an allergic reaction is an overactive response by the body’s immune system when exposed to an allergen. Allergens could range from certain foods or drugs, to seemingly harmless dust. Your body perceives these particles as harmful, triggering the release of chemicals that result in allergy symptoms.

How can I tell if I’m having an allergic reaction?

Itchy rashes or hives are the hallmark traits of an allergic reaction, says Dr Chew. Other symptoms may include itchy and watery eyes, nasal congestion, hives (itchy skin), vomiting and abdominal pain.

Allergic reactions to drugs and food can affect your skin, breathing, digestion and heart in similar ways. Symptoms are not usually distinguishable between the different allergies. Only a prick test or a blood test can diagnose your allergy accurately.

The most severe form of an allergic reaction is anaphylaxis, which comes with symptoms such as shortness of breath, repetitive coughing, a weak pulse, hives, throat tightness, and difficulty swallowing.

Symptoms may also include hives, rashes, or skin swelling combined with vomiting, diarrhoea or abdominal pain. Anaphylaxis can lead to shock and death if left untreated.

A common trigger for allergic reactions is food. Food allergies usually cause some sort of allergic reaction each time the trigger food is eaten. Some common trigger food are:

Peanut / tree nut

Peanut allergy was previously believed to be lifelong but recent research has shown that about 20% of peanut allergy sufferers eventually outgrow it. Up to 40% of individuals allergic to peanuts often show a reaction to at least one tree nut.

Symptoms for peanut and tree nut allergies are similar. They include:

  • Hives
  • An itching sensation around the mouth and throat area
  • Nausea
  • Runny nose
  • Breathlessness
  • Diarrhoea
  • Anaphylaxis


This occurs when the body’s immune system becomes sensitised to the protein in egg whites or yolks. About 70% of children with this allergy outgrow the condition by age 16. Allergy symptoms include:

  • Hives
  • Shortness of breath
  • Stomach pain
  • Anaphylaxis


Corn, corn-derived products, and even corn pollen exposure can trigger this form of allergy. A corn allergy can be tricky to diagnose because the symptoms are highly similar to those triggered by grass pollen and other seeds and grain. In this case, eliminating different types of food for a period of time might be the best way to determine whether a corn allergy is present. Corn allergy symptoms include:

  • Hives
  • Nausea
  • Stomach cramps, vomiting or diarrhoea
  • Stuffy or runny nose
  • Asthma
  • Sneezing
  • Headaches
  • Anaphylaxis


Shellfish allergies are the most common form of food allergy. There are two main kinds of shellfish: molluscs and crustaceans. More people are allergic to molluscs than crustaceans, but nonetheless it is better to avoid all shellfish altogether. Allergy symptoms include:

  • Vomiting
  • Indigestion, stomach cramps or diarrhoea
  • Hives
  • Breathlessness and wheezing
  • Repetitive cough
  • Swelling of the tongue and/or lips, trouble swallowing
  • Weak pulse
  • Pale or blue colouring of the skin
  • Dizziness or confusion


Fish and shellfish do not come from the same families of foods. Being allergic to one group does not necessarily mean you have to avoid both. Of all the types of fish available, the most common fish types which people are allergic to are salmon, halibut and tuna. Allergy symptoms include:

  • Hives
  • Nausea
  • Stomach cramps, indigestion, vomiting
  • Diarrhoea
  • Headaches
  • Asthma
  • Anaphylaxis


Milk allergy and lactose intolerance may need you to stay away from dairy products but these conditions are not related. Milk allergy is caused by an over-reactive immune system towards dairy products while lactose intolerance is an inability to digest the proteins in milk due to an enzyme deficiency.

Although some people with milk allergy can tolerate products containing dairy after they have been extensively heated, it is still best to avoid dairy products altogether and substitute it with soy or rice milk. Milk allergy symptoms that occur immediately are:

  • Hives
  • Wheezing cough
  • Nausea
  • Anaphylaxis

Delayed allergic symptoms can also occur, such as:

  • Mucus in the nose or lungs
  • Upset stomach
  • Coughing
  • Abdominal cramps
  • Loose stool or diarrhoea that may contain blood/mucus

Drug allergies

Apart from food, drugs can also trigger an allergic reaction. Common drugs that cause allergic reactions are:

  • Penicillin
  • Aspirin, ibuprofen and nonsteroidal anti-inflammatory drugs (NSAIDs)
  • Chemotherapy drugs
  • Medications for autoimmune diseases

Drug allergy symptoms usually occur within an hour of taking the drug, although some reactions occur days or even weeks later. Symptoms include:

  • Hives
  • Fever
  • Breathlessness and wheezing
  • Swelling
  • Runny nose
  • Itchy, watery eyes
  • Vomiting
  • Nausea and abdominal cramps
  • Anaphylaxis

What to do when an allergic reaction occurs

Recognising an allergic reaction is key to ensuring your safety. Dr Chew advises to take these steps when an allergic reaction occurs:

  • Call an ambulance
  • Ask the patient if they are carrying an epinephrine autoinjector (EpiPen). Press the autoinjector against their thigh to administer the epinephrine dose
  • Have the patient lie still on their back
  • Loosen tight clothing and cover the patient with a blanket
  • Don't give the patient anything to drink. If there's vomiting or bleeding from the mouth, turn the patient on their side to prevent choking
  • If there are no signs of breathing, coughing or movement, begin CPR. Do uninterrupted chest presses (about 100 every minute) until paramedics arrive

It is important to seek emergency treatment even if symptoms start to improve. Head to the accident and emergency (A&E) department immediately once symptoms occur, as it is possible for symptoms to recur even after improving. A doctor will be able to diagnose if the reaction is caused by a certain food or drug, so that you can avoid future incidents from happening.

Article reviewed by Dr Chew Huck Chin, respiratory medicine specialist at Mount Elizabeth Novena Hospital, Singapore.

1. Types of Food Allergy | Symptoms & Treatment | ACAAI Public Website. (n.d.). Retrieved from http://acaai.org/allergies/types/food-allergies/types-food-allergy

Chew Huck Chin
Respiratory Physician
Mount Elizabeth Hospital

Dr Chew Huck Chin is a respiratory physician at Mount Elizabeth Novena Hospital and Gleneagles Hospital, Singapore. He has special interests in intensive care medicine, bronchoscopy and non-invasive ventilation.