The causes of tooth discoloration and yellowing are mainly divided into endogenous and exogenous causes. And the yellowing of teeth of our smokers usually belongs to exogenous coloration. Due to the existence of a variety of bacteria on the surface of the teeth, they secrete many sticky substances. When people smoke, certain minerals in the smoke stains will be adsorbed on these sticky substances, gradually turning the teeth yellow or black. For exogenous stained teeth, in addition to smoking, coffee, tea, and red wine may also be tooth killers. According to statistics, there are 15% to 25% of smokers in China, and many of them are female smokers. That is to say, 200 to 300 million people in China have yellow and black teeth. If you want to completely solve the yellow teeth caused by smoking, you must eradicate exogenous substances, that is, try to quit smoking; then, you must find a way to make your teeth whiter. Teeth whitening is essentially a procedure to remove stains and pigment from tooth enamel and enamel. For the yellow teeth caused by smoking, we can go to the hospital for a cold light whitening. The principle of cold light whitening is to penetrate the drug into the tooth tissue through cold light, so as to achieve the whitening effect. It is a type of chemical bleaching, which is extremely harmful to the tooth enamel, and it is easy to cause the dentin to lose the necessary protection and suffer from heat and cold allergies. Exogenous pigmentation, endogenous pigmentation, etc. are more suitable for cold light whitening. It has the advantages of fast, safe, long duration and remarkable effect. The operation time of whitening is not very long, only 30 minutes. The low temperature cold light completely avoids the stimulation of the tooth nerve during the operation. Hydrogen peroxide, the main ingredient in whitening agents, has been used safely for decades to bleach teeth. In the process of whitening with hydrophilic drugs and no contact with the gums, it will not cause any damage to the tooth structure and enamel. The one-time, non-irritating, side-effect whitening effect can last for more than two years. Therefore, it is recognized as the most effective and safest tooth bleaching and whitening technology. There are many teeth whitening products on the market, and dentists recommend not to use them casually. Because the teeth whitening products on the market are prone to cause allergic reactions and adversely stimulate the teeth. Therefore, if a friend who smokes yellow teeth wants to whiten his teeth, it is best to go to a professional medical institution for treatment.