What Are Allergic Rhinitis and Chronic Rhinosinusitis?

Allergic rhinitis and chronic rhinosinusitis both affect the nose (as indicated by the prefix “rhin”):

• Allergic rhinitis describes inflammation of the inside of the nose caused by a person coming into contact with something that they are allergic to. Inflammation is a normal process through which the body responds to an injury or infection by causing blood cells and other substances to gather at the affected area. If someone is allergic to something, their immune system identifies it as potentially harmful and inflammation is triggered in an attempt to remove it. Common causes of allergic rhinitis include dust, mold spores, pollen (this form of allergic rhinitis is more commonly known as hay fever), contact with animals, and chemicals used to maintain the quality of the water in swimming pools.
• Chronic rhinosinusitis is also caused by inflammation, but specifically describes inflammation of the sinuses that is not necessarily caused by an allergy and that lasts longer than 12 weeks, even with treatment. Although it is not yet known how inflammation of the sinuses becomes chronic in some people, smoking, having a weakened immune system, the presence of growths (known as “nasal polyps”) in the nose, and allergies and related conditions like asthma have all been shown to be associated with it.

What Are the Sinuses?

The term “sinus” is used in medicine to describe more than one thing, but one use of the term is to specifically describe air-filled cavities inside the skull that are connected with each other. The role of the sinuses is not fully understood, but their presence means that the overall mass of the skull is less than it would be if it was entirely made up of bone.

Both the sinuses and the inside of the nose are lined by membrane layer that produces and secretes mucus (snot). Mucus is a sticky liquid that contains water, salt, and cells that are produced by the immune system. It keeps the nasal passages lubricated, and also protects the body from irritants (like dust and pollen) and microbes that can cause infections. If a microbe or irritant enters the nose, it gets trapped in the sticky mucus and the body then tries to get rid of it, for example by sneezing. If you have a cold or an allergic reaction, more mucus is produced than normal because the body is trying to get rid of the microbes or irritants that are causing the immune system to mount a response.

How Do Allergic Rhinitis and Chronic Rhinosinusitis Differ?

The symptoms of allergic rhinitis often develop quickly after a person comes into contact with something they are allergic to, and are similar to those caused by having a cold: a runny or blocked nose, a cough, sneezing, and the eyes may become reddened, itchy, or watery. People with chronic rhinosinusitis often have similar symptoms, and because the condition keeps mucus from draining away, they can also experience swelling resulting in pain and tenderness around the forehead, nose, eyes, or cheeks. Other symptoms include aching in the teeth, bad breath, and ear pain. The key difference between the two conditions is the length of time over which a person experiences symptoms, with the symptoms of chronic rhinosinusitis lasting much longer.

How Common Are Allergic Rhinitis and Chronic Rhinosinusitis?

Allergic rhinitis and chronic rhinosinusitis are both common. Allergic rhinitis is estimated to affect up to 40–50% of the world’s population, while studies of chronic rhinosinusitis have estimated that it affects between 5 and 12%. Although the prevalences of both conditions differ between countries, global incidence is increasing and has been linked to increased environmental air pollution, climatic factors such as humidity and increased exposure to particles carried by winds, and lifestyle factors such as increased exposure to allergens and changes in the foods that people eat.

What Did the Study Investigate?

The authors of this article analyzed data collected as part of a large, national study conducted in South Korea called the Korea National Health and Nutrition Examination Study (KHANES), which was begun to enable the health and nutrition status of thousands of Korean citizens aged 1 year or older to be monitored over a long period of time. Studies like this enable researchers to identify changes in the health of a population and to identify things that may increase the risk of developing conditions like allergic rhinitis and chronic rhinosinusitis.

The authors analyzed data relating to a group of adult KHANES participants over a period of 24 years (between 1998 and 2021) to see how the incidence of allergic rhinitis and chronic rhinosinusitis changed. They found that the incidence of allergic rhinitis and chronic rhinosinusitis increased by more than 3% and more than 2%, respectively, over the course of the study. These findings mirror those of studies conducted in other countries.

How Did Incidence Change during the COVID-19 Pandemic?

The authors also observed that the rate at which the incidence of allergic rhinitis and chronic rhinosinusitis increased slowed down between the start of the COVID-19 pandemic in 2020 and 2021. COVID-19 is caused by a virus called SARS-CoV-2, which is mainly spread via small “respiratory droplets” (so small that you cannot see them) that are released into the air when a person infected with the virus breathes, coughs, speaks, and sneezes. Although South Korea did not experience a lockdown like some other countries, the wearing of face masks and eye protection, as well as social distancing, frequent hand washing, and disinfection of surfaces was quickly and widely adopted.

Other studies have reported that such lifestyle measures, which limit the spread of SARS-CoV-2, are also useful in the management of patients with allergic rhinitis. In addition, reductions in air pollution as a result of lockdowns have been reported by some researchers to have had positive effects on people with allergic rhinitis and chronic rhinosinusitis. Although more research is needed, the authors conclude that the reduced incidence of allergic rhinitis and chronic rhinosinusitis seen in South Korea during the pandemic indicates the potential for lifestyle changes like these to benefit people with these conditions.