Causes of post-nasal drip can include:
- Bacterial infections
- Vasomotor rhinitis (overly sensitive nose)
- Medications that thicken mucus
- Gastroesophageal reflux
Thin clear secretions can be due to colds and flu, allergies, cold temperatures, bright lights, certain foods or spices, pregnancy, and other hormonal changes. Various drugs (including birth control pills and high blood pressure medications) and irregular nose cartilage can also produce increased mucus.
Thick secretions in winter often result from dryness in heated spaces. They can also come from sinus or nose infections and allergies, especially to foods such as dairy products. If thin secretions become thick, and turn green or yellow, it is possible that a bacterial sinus infection is developing.