There are many reasons why your teeth lose their whiteness. The most common reasons for dental discoloration are:
Genetics: Normal teeth may be shining white or even have a pale undertone of yellow, brown or grey, or they may be more severely stained; it all depends on your genes. Visible discoloration due to genetic dental abnormalities generally occurs in a tooth's "dentin," the material that lies beneath a tooth's enamel surface. These can sometimes be improved by whitening, sometimes not.
Physical causes: Everyday wear and tear and illness can also cause teeth to stain. Regular use of cola drinks, medications, tea, coffee, cigarettes and other tobacco products may cause surface staining, however, people with this normal kind of discoloration are good candidates for teeth whitening, except in specific instances.
