A toothbrush may look harmless, but using the same one for too long can expose you to serious health risks. Dentists warn that an unclean or worn-out toothbrush can harbor harmful bacteria that not only cause gum disease but may also increase the risk of heart disease and diabetes. Studies show oral bacteria can enter the bloodstream, triggering inflammation that affects vital organs. Experts recommend changing your toothbrush every three months to maintain good oral hygiene and reduce the risk of systemic diseases.