Why do we catch cough and colds?

I wondered why I caught cough so quickly when I felt so healthy yesterday.  I remembered going out of the house for a moment as the rain starts pouring.  But I remembered to have read in an article that even if we soak ourselves in the rain, we do not catch cough and colds unless somebody around us have it.  I "Googled" the answer  and here's what I got.


When we’re down, depressed or stressed, our immune system lowers.  If your immune system is low, the possibility of the cold virus getting a foothold in your body increases.  The sneezing, aching and coughing are signs that your immune system is fighting the virus. This means that the cough is not the disease but the symptom.  It is in fact important to clear away our lungs with mucus that blocked the upper airway passages.  


Now I learned that I should be glad if a cough produces mucus as it is called a productive cough.  It only mean that the cough helps us clear our lungs.  The dry or unproductive cough on the other end may be a sign of mild asthma and its symptoms may include shortness of breathing, feeling of tightness in the chest and wheezing.


SO NOW,  I KNOW!