Yellow, black, dark, or brown teeth stains are due to two main factors:

Extrinsic staining

Foods and beverages contain chemicals, such as pre-chromogens, chromogens, or tannin, such as tea, coffee, red wine, soft drinks, and specific dark-colored fruit and vegetable juices. These will attack the teeth and bind to the white tooth enamel, causing yellow, black, or brown staining and making teeth appear darker.

Tar or nicotine in cigarettes: Smoking is a primary cause of yellow teeth, black teeth, or dark teeth. The toxins in cigarettes will bind to the outer layer of teeth and become ingrained, causing the teeth to darken quickly. Smoking also causes a buildup of plaque, which is the principal contributor to gum disease, tooth decay, periodontal gum disease, and many other dental ailments.

Intrinsic discoloration

Aging: Our tooth enamel naturally thins with aging, allowing pigment from food and beverages to become more easily embedded in the enamel. As a result, the teeth turn yellow, brown, or darker.

Gum and tooth injuries that darken the color of the teeth: When the gums and teeth are injured, the body reacts by producing a thicker layer of dentin to protect the original dentin from destruction. However, it can also darken the color of the teeth. Additionally, injuries to the gums and teeth can also cause blood to seep into the teeth, changing the color of the teeth.

Certain medications, such as asthma or blood pressure medications, as well as some antibiotics used by mothers while pregnant, such as tetracycline or doxycycline, as well as when infants or young children are given antibiotics during the teething period or excessive fluoride exposure, can cause teeth to darken when they grow up. In addition, those undergoing treatment for certain diseases, such as cancer, may experience tooth darkening as a side effect of cancer treatment.