Allergies are caused by an overreaction of the immune system to a particular substance, known as an allergen.1 The most common allergens include pollen, mould, dust mites, pet dander, latex and insect venom. Allergy symptoms may involve a runny or stuffy nose, sneezing, watery eyes and an itchy throat. 2 It can sometimes be difficult to determine the difference between an infection (such as a cold or flu) and an allergy (such as hayfever), as the symptoms for each can be similar. However, there are certain clues that may point to an allergy being the likely cause.
Sneezing and a runny nose can often be the first sign of both a common cold and an allergy attack. Unlike colds and influenza, allergies are not caused by a viral infection.3 A mild cold may only last for a few days, whereas a more severe infection can cause symptoms for up to two weeks. If symptoms persist for longer than this time period, they may be caused by an allergy or you may need to see your doctor. Nasal discharge may also become thicker as a cold runs its course. Both allergies and colds can be distinguished from viral infections, such as influenza, by a lack of high grade fever, significant fatigue and coloured mucous, cold or flu.4
The timing of symptoms may also help determine their cause. Unlike a viral infection, an allergy will cause symptoms that are persistent or that recur in certain situations. For example, seasonal allergic rhinitis (hayfever), which is due to an allergy to pollen, will occur in the spring, summer or autumn, when the responsible plant releases its pollen into the air. If you experience watery eyes, a runny nose, sneezing and itchy throat whenever you are around hay, leaves, or are in damp places like a basement or bathroom, you could have a mould allergy.
Pet dander is a common allergen, so take notice of symptoms that occur after touching or playing with pets, or visiting the home of a friend with animals.5