Bleeding when you suck on your teeth can be caused by gingivitis and periodontitis, gum polyps, blood system diseases and other reasons. 1. Gingivitis and periodontitis: Long-term and chronic stimulation of the gums by plaque and calculus leads to inflammation of the gums and periodontium, resulting in swelling of the gums and periodontal tissues, which may bleed when slightly touched or sucked. 2. Gingival polyps: polyp-like objects formed by proliferation of gingival papillae to carious cavities due to prolonged food impaction and stimulation of tooth defects, which may cause bleeding when teeth are sucked. 3. Blood system diseases: Leukemia, thrombocytopenic purpura and other blood system diseases can easily cause spontaneous or irritating bleeding of the gums and bleeding when teeth are sucked. Bleeding when sucking the teeth should be timely consultation, under the guidance of the doctor to clarify the diagnosis of the correct treatment. Daily attention to maintain oral hygiene, morning and evening diligently brush teeth.