To respond effectively to COVID, it's been important to understand who may be at higher risk of contracting the virus and developing more severe diseases.

To this end, scientists and clinicians have established a range of risk factors for serious illness with COVID, including older age, obesity, and several underlying health conditions. High body mass index also appears to be linked with increased odds of catching COVID in the first place.

But what about factors that might make someone less likely to contract COVID? Interestingly, research suggests that having allergies could reduce a person's risk. Allergies are very common.

At least 400 million people around the world are affected by pollen allergies or hay fever. Some 300 million people suffer from allergic asthma (induced by inhaling allergens), while food allergies affect around 250 million.

Many people are also allergic to certain drugs. Allergic reactions can range from mild (perhaps some redness and swelling on the skin) to severe (anaphylactic shock, which can cause death).

Atopic diseases is a name given to a group of conditions triggered by allergens and includes hay fever, eczema and dermatitis. Research has shown that people with atopic diseases have 25% lower odds of contracting COVID. For people with atopic disease and asthma, the risk is 38% lower compared to people without these conditions.

A separate study showed that people with food allergies were 50% less likely to become infected with COVID.

Why would people with allergies be at lower risk?

Initially, we thought that people with allergies could be less likely to contract COVID as they may have been more isolated from others. This might be true for asthma because people with this condition were advised to shield earlier in the pandemic.

But the same can't be said for the majority of atopic diseases, such as eczema. And while you might expect people with food allergies to, say, eat out less, research during the pandemic has shown that households with food allergies only had slightly lower levels of exposure in the community compared with other households.

To be able to infect the body, SARS-CoV-2 (the virus that causes COVID-19) attaches to a specific protein called the ACE2 receptor. This protein provides the entry point for the virus to infect a wide range of human cells.

Having higher amounts of ACE2 receptors is associated with increased susceptibility to COVID infection. People who smoke, have diabetes or have high blood pressure (all of which are associated with a higher likelihood of severe COVID) have more ACE2 receptors.

Meanwhile, it has been shown that type 2 inflammation a normal immune reaction that can occur in response to infections or parasites, but also occurs prominently in allergic conditions reduces ACE2 expression in the airways. This decreases susceptibility to infection and is considered the primary reason people with allergies appear to be at a lower risk of catching COVID.

There is also a range of other factors that may contribute to reducing COVID infection risk among those with allergies. For example, people with asthma tend to produce more mucus than others, which is understood to prevent SARS-CoV-2 from entering the airways.

More good news

So we see a reduced risk of catching COVID in people with allergies and asthma. But how do these conditions affect the severity of a COVID infection?

At the beginning of the pandemic, it was assumed that people with asthma may be at greater risk of getting very sick from COVID because viral infections commonly exacerbate asthma. But it's now well established that asthma that's mild or well controlled doesn't increase the risk of serious illness with COVID. And the evidence doesn't indicate more severe asthma increases the risk either.

Similarly, the atopic disease is not considered a risk factor for severe COVID. If you suffer from other diseases in combination with asthma or allergies, it's important to be aware that this could increase COVID severity.

Prevention remains key. The best ways to prevent COVID infection continue to include vaccination, wearing appropriately-fitting face coverings, and physical distancing.

Meanwhile, if you have allergies, having an allergy management plan is essential. Make sure your treatment plan is current and that you have medications on hand in case you need them.