Bleeding gums is commonly caused by gingivitis (milder gum disease) and periodontitis (more advanced gum disease). Gum disease, over the long term, may cause bleeding gums during daily activities like teeth brushing, eating, or sometimes even spontaneous bleeding. This can be commonly controlled by regular periodontal cleaning.
On rare occasions, this may be a sign of more severe problems such as blood diseases, drug interactions, diabetes, etc. A dental check-up is a good starting point to rule out other non-dental causes of gum bleeding.