What causes blood in snot?

Inflammation. The nose is very vascular (many blood vessels-including very small capillaries), and minor inflammation of those blood vessels can sometimes cause blood tinged mucus.
Bloody noses. Blood can appear in the nose from erosion of the small blood vessels in the nose due to mucus.

Related Questions

What can cause blood stained snot for at least two months off and on? I had bronchitis about two or three months ago and I've had it ever since.

Infection.sinuses. An infectionfection that spreads from your sinuses to lungs can cause blood tinger nasal discharge: not a good symptom: get an examination, including a chest xray ASAP. Read more...