Upper respiratory infections such as colds or the flu can cause irritating symptoms. One common symptom that often appears before other illness symptoms and resolves last is post-nasal drip. Post-nasal drip is a common condition that results from the over-production of mucus. It can cause irritation to the back of the throat and even lead to a cough. Keep reading to learn more about what causes post-nasal drip and how to treat it. If you ...