Whats the cause of nose bleeding ?

Depends on age: In children, the most common cause of nose bleeds is trauma or foreign body (most likely from picking with a finger). In adults, nose bleeds can be caused or prolonged by a number of factors. The most common of which would be blood-thinning medications like coumadin; plavix; Aspirin and trauma. Inherited blood clotting disorders may be a cause as well but are rare and would likely be known by you.

Various: Nose bleeds are common in dry air or with swelling of the nose (such as with a cold or allergies). They also occur with trauma or nose picking. Once there is a bleed, the scab can easily fall off, causing more bleeding. Humidify the air and add petrolatum jelly to the inner nose to help keep the scab moist as it heals. If prolonged bleeding, other areas bleeding, or easy bruising, see a doctor.