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 also the start of hay fever season – so what is the more likely affliction?
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.
One of the key differences is the colour of the nasal discharge (your snot): it's more likely to be yellowish/green in colour in colds; while in hay fever, it's clear.
Facial itchiness – especially around the eyes or throat – is a symptom typically only seen with hay fever.
If someone is allergic to a seasonal environmental trigger such as pollen, their symptoms may be restricted to particular seasons of the year. But if you're allergic to dust or smoke, symptoms may last all year long.
Hay fever, like asthma, is an allergic disease and can sometimes cause similar symptoms, such as coughing, wheezing and shortness of breath.
A sore throat, on the other hand, is generally a precursor to cold. If you have cold-like symptoms and a sore throat or have had one in the last few days, your condition is more likely to be the common cold.
What if you've never had hay fever before?
You're more likely to catch viral infections during winter when more bugs are circulating, but it's possible to catch a cold any time of the year.
It's possible to develop hay fever in adulthood. This may be due to genetic predisposition that manifests only when certain other contributing factors are present, such as a high level of airborne pollen.
Or it may be due to a major change in lifestyle, such as a move to a different location or change in diet.
Most adults will get two to three colds per year, while hay fever affects nearly one in five Australians.
Around 10-20 percent of hay fever sufferers grow out of hay fever at some point in their lives and about half find their symptoms get less severe as they get older, which means that for the majority of sufferers, hay fever can last a long time.
How are they treated?
An allergy test, using a skin prick or blood test, for allergen-specific IgE could inform you of the specific irritants that trigger your condition. These tests can be organised through your GP or pharmacist.
Oral antihistamines are effective in hay fever patients with mild to moderate disease, particularly in those whose main symptoms are palatal itch, sneezing, rhinorrhoea, or eye symptoms.
Generally, treatment isn't necessary for a cold but over-the-counter medications such as paracetamol and ibuprofen can help relieve some of the symptoms. 
Reena Ghildyal, Associate Professor in Biomedical Sciences, University of Canberra and Cynthia Mathew, PhD student, Sessional Tutor, University of Canberra.
This article is republished from The Conversation under a Creative Commons license. Read the original article.