Smoking
Nicotine from smoking doesn't just develop an unhealthy addiction; it leaves yellowish or brownish surface stains on your teeth.
Poor dental hygiene
Not brushing, flossing, and rinsing enough to remove plaque and stain-producing substances.
Genetics
Sometimes, tooth color runs in the family. If one of your parents' teeth are yellow, it's likely that yours are a similar hue. Reddish brown, reddish yellow, gray and reddish gray are four natural shades of otherwise white teeth, and this depth of color varies across a spectrum from light to dark.
Foods
A wide range of foods stain teeth. Tomatoes in pasta sauce, curry spices and berries all contain pigments that cling to tooth enamel and stain this surface.Even a healthy salad with balsamic vinegar dressing can leave an unsightly color on your teeth.
Drinks
Coffee, tea, colas, wines.Other culprits include dark and light sodas and sports drinks with artificial flavoring.
Fluorosis
Fluoride is good for teeth, but excess fluoride can cause yellow or brownish yellow spots called fluorosis. Fluoridated water, fluoride toothpaste and prescribed fluoride tablets and treatments are your biggest sources of fluoride.
Tobacco
Smokeless tobacco products like, snuff and chewing tobacco causes teeth stains.
Grinding
Tooth grinding is an unconscious habit some people have when they're stressed, especially while asleep. Also known as bruxism, it's quite harmful to tooth enamel, weakening it to the point of cracking and yellowing.
Dentin
Teeth look yellow when the enamel is thin and the dentin underneath shows through it. Dentin is a deep yellow to brownish material inside your teeth under the enamel, and it's often responsible for the yellow you see when you look in the mirror. Thick enamel covers up the dentin, but keep in mind it doesn't always block the stains that build up on the surface, another cause of yellow explained further down.
Aging
Teeth ultimately turn yellow as you get older, when enamel wears away from chewing and exposure to acids from food and drink. Most teeth turn yellow as this enamel thins with age, but some take on a grayish shade when mixed with a lasting food stain.
Accidents
Impact of an accident or physical trauma can crack tooth enamel and damage the tooth's interior, leading to discoloration that may indicate bleeding that needs professional attention.
Antibiotics
Tetracycline antibiotics stain teeth when they're developing in the gums.Antibiotics in the second half of her pregnancy, or you took them before the age of eight, you may have permanently stained adult teeth that merit an in-office bleaching treatment.