Oldie: why do we sneeze, get runny noses, and phlegm-y when we have a cold?

See topic. I don’t see connections, except everything trying to get rid of excess water, which I don’t know why we would have with a cold.

You’re assuming these bodily functions occur to help us. They don’t. The virus makes them happen to increase its odds of being transmitted.

I also saw this statement in a thread going on now.

I just find that hard to believe. I don’t have time to gather my thoughts and pose any decent questions, or cite (to me) counter examples, but this evolutionary “strategy” hit upon by these type viruses seems strange.

Sneezing, runny noses and phlegm are immunological responses to infection. The sneezing attempts to clear foreign bodies out of the nose, the rhinorrhea is to keep it contained in the nose and away from the lungs and the phlegm is to catch anything that makes it down from the nose.

When you sneeze without covering your nose, you’ve just spread your cold 20 feet for others to breathe in. Coughing; same thing. When you wipe your runny nose and then touch objects in the public domain which others then touch, they can then catch your cold.

I always took it that that was the body’s reaction to various types of irritation, in this case from a cold virus. Similarly, with allergens, such as pollen, and cold air. Just a WAG, though.

There are two parts to this, the direct reaction caused by the virus and your body’s immune reaction to the virus, which are somewhat intertwined.

When you first get a cold, you develop sneezing and a runny nose. These are direct body responses to the virus which help to rid your body of the virus but from an evolutionary standpoint also help the virus to spread. Your body is trying to get rid of the virus but at the same time you are helping the virus get to other hosts.

As your immune system kicks in, your white blood cells come to fight the virus which makes your phlegm thicker and yellow to green. That is showing that the cells are effectively on the attack and killing the virus. Your cough kicks in to help rid the body of all the dead virus and white blood cells. This is why it is a good sign in a cold when your sputum turns darker and does NOT mean that you need antibiotics. By this time most of the virus is dead and what is left is the effects of your body fighting it off.

For part one, these direct body responses are the body “thinking” that shedding water by any means necessary is the response? Is this a correct body response, insofar as it is an effective defense/counterattack? Or something triggered by an intermediary process that the virus takes advantage of?

I’m still chewing over the evolutionary propagation part. :frowning:

It doesn’t seem so strange to me. There are other diseases where the infectious agent (virus, bacteria or other) alters the behavior of the infected animal to help spread itself. One of the oddest is toxoplasmosis, which causes infected mice and rats to be attracted to the smell of cat urine (normally they are repelled by it). Another is the fungus Ophiocordyceps unilateralis, which alters the behavior of infected ants to cause them to climb up plant stems, where they clamp on with their mandibles and die, giving the fungus a good place to spread its spores.

Cold viruses do something pretty simple: they stimulate existing body responses. Coughing, sneezing and runny noses are all ways the body rids itself of foreign irritants. The viruses have evolved to exploit these responses, pushing them into overdrive. It’s a very effective way for the viruses to spread themselves.

That brings me to a question I’ve had for quite a while. If the runny nose, cough, and thickening phlegm are the body’s natural response to the infection, then what is the net effect of treating those symptoms. Are we prolonging the illness by taking decongestants, antihistimines and cough suppressants?

I’m not convinced that these symptoms are the body’s natural way of fighting a cold. In any case, the conventional wisdom with colds is that it takes about a week to get over one, regardless of what you do. Treating the symptoms seems to have no effect on the cold’s duration.

Bolding mine in both pulls.

Thanks for examples. They are extraordinary and convincing. Go Darwin!

The two bolded sentences seem to be at variance, however.

Sneezing is effective at expelling irritants like dust and pollen from the nose. Coughing is effective at expelling irritants like smoke from the lungs and throat. I’m not convinced that either is effective at expelling cold viruses from the body in enough quantity to help one get over the disease. The viruses involved in the infection are in the cells and the spaces between the cells, not just on the surface of the nose, throat and lungs. That is, coughing and sneezing do little to help one get over a cold, and do a lot to spread the cold to other people.

Another example of a human body’s response to infection that helps spread the infection is the Guiniea worm in Africa. Hopefully this will soon be eradicated through education and sanitation. Former President Jimmy Carter has been working on these efforts for years.

The worm is ingested by drinking water contaminated with infected water fleas. Once in the body the worm moves to the lower legs and causes a great burning sensation. So infected individuals seek relief by standing in water. The lesions erupt and the cycle begins again.