There are several reasons why teeth can become yellow, including:

• Age: As you age, the white enamel surface of your teeth may wear down, and the yellow core of your teeth becomes more visible.

• Food and drinks: Certain foods and drinks can stain your teeth, such as coffee, tea, colas, wines, and certain fruits and vegetables.

• Smoking: Nicotine from smoking can cause tooth discoloration and bad breath, among other things.

• Poor oral hygiene: Poor brushing and flossing habits can lead to plaque and tartar buildup, which can cause yellowing on your teeth.

• Genetics: Some people may have genetically yellow teeth due to thin enamel that allows the yellow dentin underneath to show through.

• Medication: Certain medications, such as antihistamines, high blood pressure drugs, and chemotherapy, can cause tooth discoloration.

• Disease and treatments: Several diseases that affect enamel and dentin can lead to tooth discoloration, and treatments for certain conditions can also affect tooth color. For example, head and neck radiation and chemotherapy can cause teeth discoloration.

To prevent yellow teeth, it is recommended to brush and floss regularly, avoid smoking, limit consumption of staining foods and drinks, and visit the dentist regularly for cleanings and checkups.