Hello sonakshi, bleeding gums are caused by the condition named "gingivitis". In simpler terms, it is inflammation of gums (gingiva). In this condition the gums bleed while brushing or chewing. In gingivitis, gums swell and become prone to bleeding on slightest provocation such as brushing. The most common cause for this condition is the accumulation of plaque and calculus (tartar) on teeth. The treatment simply includes cleaning of teeth by professional dentist (scaling). However, in certain patients, gingivitis may occur in the presence of underlying periodontitis (inflammation of tooth supporting structures such as PDL, alveolar bone) and this requires aggressive periodontal treatment such as flap surgery.