Whitening is purely for looks and doesn’t affect your bite.
Babies and children really do have pearly whites, but as people age, their teeth can become stained or yellowed. Coffee, tea, and red wine are particularly likely to cause severe stains, as they contain chemical compounds called chromogens that leave pigments in the tooth enamel.
Enamel tends to wear down and become thinner with age, which allows the yellowish underlayer, or dentin, to show through. Tobacco, whether smoked or chewed, leaves yellow or brownish stains on the teeth. Radiation therapy, chemotherapy, and some medications may also stain the teeth.