It is possible to whiten your teeth somewhat without resorting to commercial products. Although, the effects will not be as dramatic and will not happen as quickly.
Obviously, if you are concerned about yellowing of your teeth, you should try to avoid coffee, tea and smoking.
Try using baking soda(sodium bicarbonate) instead of toothpaste. Using baking soda to very gently brush your teeth helps keep them polished and white. Sodium bicarbonate can, also, help to replenish the lost mineral content of the teeth, which helps them to regain their whiteness.
Certain foods are believed to be natural tooth whiteners. Cranberry juice, tomatoes and celery are tooth whitening foods. Foods containing a high concentration of Vitamin C help to keep yellow-appearing plaque off your teeth.
Rubbing an orange peel on your teeth is an old folk remedy for whiter teeth. Eating strawberries or crushing them and using the berries as a tooth paste is another common remedy for naturally whiter teeth.
Spearmint is a natural plaque-fighter. Rinsing your mouth with a drop or two of natural, food grade spearmint oil is another natural way to whiten your teeth.
In centuries past, Europeans used honey and vinegar to whiten their teeth. Alternatively, after brushing, try rinsing your mouth with a solution of three parts lemon juice and one part sea salt.
One of the most popular and powerful natural whiteners is hydrogen peroxide. It is also a powerful anti-bacterial and helps you to have an overall healthy mouth, naturally. Put a few drops of hydrogen peroxide on your toothbrush whenever you brush your teeth. You can also use diluted hydrogen peroxide as a tooth-whitening mouth rinse.
Again, these methods of tooth whitening do not give the fast and dramatic results of commercial products, but over time they can help to keep your teeth healthier and whiter.