A-choo! Here comes another day of living with allergies. We are all familiar with the coughing and sneezing, but what exactly are allergies and what causes them?
Every day, our bodies are in constant contact with potential threats. These include pathogens (harmful microorganisms), pollution, and a host of other dangers. However, most of the time, we aren't even aware that anything nasty has entered our bodies. How are we able to combat these invaders so effectively? We have our immune system to thank. Immune cells called lymphocytes (pronounced lim-fo-sites) patrol all parts of the body looking for foreign molecules and microorganisms (tiny living things, like bacteria). Each lymphocyte is programmed to recognize a specific pathogen. Anything which is not part of our body is classified as "non-self" while every one of our own cells is termed "self." In short, the role of the immune system is to attack and destroy any cells it finds which are "non-self."
We also have sensors in our bodies which can detect the presence of harmful chemicals. Have you ever walked by a car and coughed or sneezed as you smelled the exhaust? This is because you have sensors in your nose, throat, and lungs that tell your brain that you have inhaled dangerous fumes, which you need to get rid of right away. So, your body sends the signal to cough and sneeze until you push out all of the fumes. This signal is sent by a chemical messenger called histamine.
If you have allergies, or know someone who does, then you might agree that the symptoms of allergies are kind of like a huge overreaction to the car fumes, except without the car! People with allergies react as if they have inhaled something toxic when in fact they have just inhaled normal everyday things like pollen and dust that are not harmful (these everyday substances are called allergens). This occurs because some of their lymphocytes are programmed to recognize the allergen as a harmful substance even though it is not. So, when the lymphocytes find an allergen floating around in your body, they trigger histamine to be released which causes the common allergic symptoms such as watery eyes, runny nose, sneezing and coughing (these are all ways to flush out the allergen). Histamine also triggers local swelling near the pathogen or allergen, and so it can cause narrowing of the airways (nose and throat) when you inhale pollen or dust in order to prevent more of the allergen from entering the lungs. Unfortunately, that makes it harder for the person to breathe (fun fact: histamine is also responsible for asthma - can you see the connection?).
So how can we treat allergies? The primary method to prevent allergic symptoms is to treat the person with antihistamines, which have been used since the 1930s to control allergies. The medicine does not affect the lymphocytes, but rather it just prevents histamine from triggering its bothersome symptoms.