You wake up with a runny nose and, come to think of it, you’ve been sneezing more than usual. It feels like the start of a cold but it’s October – the start of hay fever season – so what is the more likely affiliation?
Hay fever and colds are easy to confuse because they share the clinical category of rhinitis, which means irritation and inflammation of the nasal cavity.
The mechanisms share some similarities too, but there are some key differences in symptoms – notably, itchiness and the colour of your snot.
Similar mechanisms.
The common cold is a viral infection of the upper respiratory tract, usually caused by rhinoviruses. Colds spread easily from one person to the other via coughing, sneezing and touching infected surfaces.
Hay fever, on the other hand, can’t spread from person to person. It’s an allergic response to an environmental irritant such as pollen or dust.
The nasal cavity contains cells that recognise foreign substances such as bugs and pollen. Once the body detects a bug or irritant, it activates an army of T cells that hunt down and destroy the substance. This is known as an immune response.
In hay fever, the irritant triggers the same immune cells as viruses. But it also causes the release of IgE antibodies and histamines to produce an ongoing blocked nose, impaired sense of smell, and nasal inflammation.
How you tell the difference.
Both hay fever and the common cold causes sneezing, runny or stuffy nose and coughing.