My 15 yo son has had 3 nosebleeds in a 3 day time frame. no cold not sick. what could be some reasons for frequent nosebleeds?

Epistaxis: Nosebleeds are common in children. Approximately thirty percent of children younger than five years and over half of those aged 6 to 10 years have had at least one nosebleed. Nosebleeds are more common during cold weather and when ambient humidity is low. Common causes of nosebleeds in children include trauma, dry air, nasal foreign body, and rhinitis. If persistent an ENT evaluation is indicated.