A runny nose may not be the worse thing you can experience, but it can be very inconvenient and irritating. A runny nose is actually a symptom of some other condition. We normally associate a runny nose with a cold, but it can also be due to allergies.
The physiological explanation for a runny nose is rather simple - the sinus and nasal passages become overactive and produce more mucus than usual. It is that excess mucus that makes your nose runny. What causes the over production of mucus? It can be that your body is fighting off the flu virus or a cold. It could also be an allergic reaction to dust, pollen, or some other irritant.
When treating a runny nose, it is important that you know the underlying cause. If you have a cold, or you feel that you are coming down with the flu, then over-the-counter medication for these ailments will help. If you experience a runny nose often, then you might be allergic to something. You need to determine what the cause is so that you can treat that immediately. In general though, you can take antihistamines. This will stop the production of mucus.
Of course, you can always go the old fashioned way - always have a box of soft tissues with you so that you can blow your nose. This works excellently, but you also need to blow your nose gently in order to avoid irritation. Additionally, there are nasal saline solutions that help flush out your nasal passages.