Help please. Why does my 9 years old nose bleeds from one nostril at-least once !

Help please. Why does my 9 years old nose bleeds from one nostril at-least once a month?

I make him lie down and soak his head with cold water and put
a napkin on his face, it stops sometimes within 10 minutes.
He does not pick his nose, nor any injury or tedious work out nor he is allergic to any medicine or environment.

i used to have the same problem when i was younger. mine would come about with dry air, extreme change in temp, or any slight bump on the nose. first of all....DO NOT make him lay down or put his head back! to stop the bleeding, have him sit up with his head down towards the floor, pinch the tip and the bridge of his nose and place a cold rag on the back of his neck, this should stop the bleeding very quickly. to prevent the bleeding you can try a humidifier, or use a q-tip to apply a small amount of vaseline in his nostrils, this will prevent the inner walls from drying and cracking which is what usually causes the bleeding! you may need to talk to you doctor about having his nose "cauterized" not sure of spelling but they put a q-tip in his nose that has chemicals to "burn" the nerve endings and seal them. i had this done, it wasn't a pleasent experience but it worked! the nose bleeds stopped. good luck!