My son occassionally has bleeding nose. is this normal ? is there a health risk in the long term?

Common: Epistaxis is common in everyone. 80% of people experience this in their lives. A common cause is dry, hot air like inside the home in the winter causing nasal dryness and crusting. The nasal tissue cracks and bleeds easily. Treatment includes humidification of the air, and nasal moisturizing with a variety of otc nasal saline gels or mist spray. It's not a major health hazard, but should see md.

Maybe: Nosebleeds can be caused by so many things, ranging from benign things (nose picking, dry air, etc) to chronic conditions (bleeding/clotting problems) to terrible things like cancers. I would start with simple things like a humidifier and some vaseline at least twice a day. If it doesn't get better, it's time to take him to see a doctor for some tests and an examination.