My 11 year old son gets a lot of nose bleeds especially in the last 5 days. what is causing this?

Usually irritants : Nose bleeds are usually a reflection of nasal irritant effect. Dry heat, smoke, dust, fumes, etc.All lead to irritation and occasionally infection.This causes small nasal capillaries to bleed, often as the face is rubbed into bed linen in sleep. Removing as many irritants from their life as possible can help as can nasal saline wash, nasal saline gel and humidity within their sleeping areas.