You’ve been through winter lurgies and escaped the start of spring free of hay fever. Now you wake up with a sniffle you can’t seem to shake.

How do you know if it’s hay fever, a cold, or something else? And how do these two different culprits cause such similar symptoms?

Hay fever is actually an allergy

Hay fever is an allergic reaction to tiny particles you inhale from “allergens”. These might be pollen, house dust mites, or animal dander (dead skin cells).

Normally, the body won’t respond to these harmless particles. But for some people, the immune system mistakes them for something dangerous.

If you have allergies, your immune system prepares a particular type of antibody, called IgE, to target the culprit allergen.

Histamine and other inflammatory substances inflame the lining of your nose, eyes and throat (Getty/iStock)

When you’re next exposed to that allergen, such as grass pollen, your immune system quickly releases chemicals such as histamine, which contributes to an allergic reaction.

Histamine and other inflammatory substances that are released inflame the lining of your nose, eyes and throat. This causes sneezing, a runny or blocked nose, itchy eyes, feeling drained and having trouble concentrating.

Histamine irritates the nerves in your nose, eyes and sometimes your throat or skin, causing the itch. It’s your body’s false alarm, thinking it needs to protect you.

A blocked or runny nose can make breathing at night difficult, affecting your sleep, leaving you tired the next day.

How the body defends against a viral attack

When you catch a cold, viruses enter your body via inhaled droplets or aerosols, landing onto your nose or throat. The viruses use the coating on their surface to attach and enter the cells lining your nose and throat.

That is where a cold virus can replicate, and burst the infected cells to spread and infect more cells in the vicinity. This causes the release of molecules that signal to other immune cells to come to the infected area, and fight the viruses.

During the fight, chemicals including histamine (yes, similar to a hay fever response) and other chemical mediators are released, causing symptoms such as a stuffy, runny nose, sore throat, sneezing and, sometimes, a fever.

Many respiratory viruses can cause cold symptoms: common cold viruses (rhinoviruses), coronaviruses (the non-SARS kind), adenoviruses and more significant ones such as the flu (influenza), respiratory syncytial virus (RSV) and COVID (caused by SARS-CoV-2).

So how can you tell the difference?

While hay fever and cold viruses share some overlapping symptoms, one of the main differences is that, ironically, hay fever doesn’t actually cause a fever, but a cold- or flu-like virus sometimes does.

Other cold or flu symptoms not commonly seen with hay fever could include a sore throat, muscle aches and pains (particularly influenza), and cough with thick mucus (known as sputum).

However, if hay fever is associated with asthma, you might also have a cough and feel breathless.

Colds don’t usually cause itchy eyes (Alamy/PA)

Feeling itchy – and itchy eyes in particular – is a prominent symptom of hay fever, not commonly seen with colds.

Duration and triggers for symptoms can also be a clue. Cold or flu symptoms may resolve within a week or two, with the season typically peaking during winter.

Hay fever symptoms may last for the duration of the spring to summer pollen season (seasonal hay fever), or whenever the person is exposed to the particular allergen that triggers them.

What do you need to watch out for?

Untreated hay fever can have significant impacts on quality of life and performance at work and school. Symptoms can persist for months and recur yearly with allergen exposure, particularly grass pollen.

If hay fever occurs alongside uncontrolled asthma, serious complications such as asthma attacks, may require hospitalisation.

Thunderstorms during high pollen counts can also cause “thunderstorm asthma”, even if you’ve never had asthma before.

Cold viruses usually resolve on their own with rest, fluids and pain relievers such as paracetamol.

However, influenza, SARS-CoV-2 and RSV can cause complications for those with compromised immune systems, young children, pregnant women, older people and those with underlying lung diseases. Complications can include pneumonia (severe lung infection), bronchitis/bronchiolitis (inflamed airways) and even death, so early health care can be crucial.

Why you might get both at the same time

Being exposed to allergens can weaken the immune response in the cells lining your airways. This makes it harder for your body to fight off respiratory viruses, meaning colds can last longer and feel worse.

High levels of airborne pollen have been linked to more hospital admissions for asthma in boys infected with rhinovirus (a cold virus) and even to rises in SARS-CoV-2 (COVID) cases.

About the authors

Janet Davies is the Respiratory Allergy Stream Co-chair, National Allergy Centre of Excellence; Professor and Head, Allergy Research Group, Queensland University of Technology. Joy Lee is a Respiratory Allergy Stream member, National Allergy Centre of Excellence; Associate Professor, School of Translational Medicine, Monash University. Saeideh Hajighasemi is a Postdoctoral Research Fellow at Queensland University of Technology.

This article was first published by The Conversation and is republished under a Creative Commons licence. Read the original article.

Pollen carries a variety of bio-molecules, each of which can directly affect the cells lining our respiratory tract, and possibly facilitate respiratory viral infection.

However, other studies suggest hay fever might actually be a protective factor against severe COVID. This highlights how complex the relationship is between pollen, our immune system and respiratory viruses.

What should we do to control symptoms of allergy?

The best way to treat hay fever symptoms is with a nasal steroid spray, or a steroid spray combined with an antihistamine. Oral antihistamines aren’t as effective at controlling underlying inflammation as nasal steroid sprays.

Reducing or minimising exposure to allergens where possible can be useful, in Australia, daily pollen information can provide an alert on high pollen days.

Testing and further allergy treatment such as immunotherapy may be available with an allergy specialist. Immunotherapy is the process of “desensitising” the immune system so it’s less likely to over-react to triggering allergens.

If you also have asthma, see your doctor to review and update your treatment plan and preventer inhaler every year.