thanks for your reply, i drink a lot of water everyday. The problem is my wife have the same symptom as mine! We both really drink a lot of water. And I forget to tell you guys that i did apply lip balm, but the corner of my lips seem not respond to the lip balm, it will still crack, and in the morning, i recently notice that some white thing at the both corner if my lips. I suspect i was infected oral yeast. I did perform unprotected oral sex on a lady 10 weeks ago, i aam not sure whether that lady had vaginal yeast infection. I had make an appointment to see a dermathologist next monday, hopefully can dignose some thing out.