I have a bad runny nose – how do I know if it;s from cold or allergies. Posted on December 31, 2018March 8, 2023 by 0 Vote Up Vote Down Ask A Doctor Staff asked 4 years ago I have a bad runny nose - how do I know if it;s from cold or allergies. 1 Answers 0 Vote Up Vote Down Ask A Doctor Staff answered 4 years ago A cold will usually last no longer than two weeks. If you are experiencing a runny nose from allergies, the symptoms will last as long as the allergen (pollen, dust, pet dander, mold, smoke, environmental pollutant) is no longer around. Please login or Register to submit your answer Username or Email Address Password Remember Me