One of the most common causes of nosebleeds in adults is dry air, as nasal passages are more susceptible to bleeding and infections as they dry out, according to Mayo Clinic. Trauma to the nose is another common cause, states WebMD.
Trauma to the outside of the nose, such as a sharp blow to the face, and trauma to the inside of the nose, such as irritation from a cold, can both cause nosebleeds, states WebMD. More rarely, nosebleeds may be a sign of an underlying condition, such as the inability of a person's blood to clot. Conditions such as kidney disease or taking blood-thinning medication can cause a person's blood to stop clotting properly. High blood pressure may contribute to the bleeding but is seldom the sole contributing factor.
Other diseases that cause nosebleeds are allergies, sinusitis and a deviated septum, according to Mayo Clinic. Foreign bodies in the nose and chemical irritants can also cause nosebleeds. Even more rare are conditions such as nasal polyps, leukemia, sarcoidosis and nasal tumors.
While most nosebleeds are not serious and stop on their own, a person should seek immediate emergency care if she experiences trouble breathing due to the bleeding or the bleeding results from a serious injury, states Mayo Clinic. An individual should also seek medical help if the bleeding does not stop after 30 minutes of care.