What causes flem inthe chest?

Inflammation: Phlegm can be produced by inflammation in the chest. That could be underlying asthma or exposure to dust or chemicals. It can also be caused by viral or bacterial infections. Certain allergies can also cause production of phlegm.

Find a cause: Phlegm is just mucus. It can come from infection, inflammation, irritation in the lung or from dripping that only seems to come from the chest. Best to get to your own doctor so that s/he can talk with you about whether any additional investigation, testing or referrals are needed to get to the bottom of the question.