9 Causes of Bleeding Gums When You Brush Your Teeth

Gingivitis 

Gingivitis usually develops when plaque stays on gums lines for too long. Plaque is the debris and bacteria that stick to your teeth. Brushing your teeth twice a day can remove plaque and can prevent cavities. But plaque is able to stay on your gum line if you do not brush and floss correctly. The plaque that is not removed correctly accumulates and can cause gingivitis. The plaque hardens and turns into tartar (calculus) which is what increases the bleeding.