Good question!

A persistant cough could be due to a bunch of things including asthma and gastroesophageal reflux disease (GERD), which is also known as acid reflux (you know, the condition in those "purple pill" commercials).

First, the best thing to do is to ask your doctor who can run tests and tell you just what is causing your cough.

Second, what's causing your cough may depend on what your cough is like. Coughs caused by acute bronchitis, tend to look like this:

It is steady or gets increasingly worse for 10 days to 2 weeks
Worse at night
Starts out dry and irritating, but becomes increasing loose over time
May cough up mucus
Lasts for less than 6-8 weeks

Cough associated with chronic bronchitis, is more like this:

A lot like acute bronchitis coughs, but produces mucus (sputum), which may be blood streaked
Shortness of breath aggravated by exertion or mild activity
Last longer than 8 weeks

Does this sound like you? You can also check asthma symptoms and GERD symptoms -- chronic cough is associated with those too.

Be sure to talk to your doctor if you have a cough that you can't shake!