What is a common cause of nosebleeds (epistaxis)?

A common cause of nosebleeds, or epistaxis, is indeed dry air or trauma. The nasal mucosa is sensitive and can easily become irritated or damaged. When the air is particularly dry, as often occurs in winter months or in arid climates, the mucosal lining in the nose can dry out, leading to cracks and bleeding. Additionally, physical trauma, such as nose picking or a direct blow to the nose, can also cause small blood vessels to rupture, resulting in a nosebleed.

While other factors, such as high blood pressure, nasal polyps, and sinus infections, may contribute to bleeding in some cases, they are not as common or immediate causes as the irritation from dry air or direct trauma to the nasal passages. These latter factors may complicate or exacerbate the frequency of nosebleeds, but the primary and most frequent triggers are generally associated with environmental conditions and physical injury.