Three of the things a physician looks for in distinguishing between coughs are whether the coughing is chronic, productive and blood-tinged.

Chronic:  if the coughing goes on and on, lasting not for two days but for weeks or months then it should be investigated.  Chronic, so-called "smokers" coughs" are often evidence of bronchitis but sometimes are symptoms of cancer.

Productive:  this means the person is producing or bringing up anything in the cough.  Mucus production can accompany colds and allergies, with greenish or yellowish material which may actually be pus can signal lung infections which need to be treated.

Blood-tinged:  this can be a serious signal that something is wrong and should not be ignored.  Blood-tinged sputum does not always denote real problems, but infections like TB or lung cancer can show up as coughing with blood-tinged sputum.  And the sooner these conditions are attended to, in general, the greater the chance for complete cure.  For a copy of this script, access our web site, speakingofhealth.com.  Speaking of Health, I'm Dr. Steven Andrew Davis, for CBS News.