A constant cough. In most cases, cough is the main symptom of colds, flu, pneumonia, etc. But do not take a cough as an insignificant sign. A cough can be dry, for example, as with allergy, or soggy, for example, as with influenza and colds. The mucus can be dyed orange, red or brown, or you can even detect blood in saliva. In any case, an emergence of a chronic cough for a long time is a substantial reason to consult a doctor.