Teeth become yellow over time because of 6 major factors : red wine, coffee/tea, soda, cigarettes, candy and antibiotics. So if you think you take too much of these products, maybe you should start decreasing your intake.
There’s plenty of whitening kits available. The problem is, they are often way beyond our means. So i looked up for an efficient alternative that everyone can afford. And i have found it! The only ingredients you will need are lemon and baking soda!
Make sure you don’t overdo whitening treatments, because it will weaken the enamel.