Over time, our teeth will definitely change color and will not be bright white forever. Tooth discoloration is also a normal thing for anyone to experience, for example due to aging or diet. Meanwhile, abnormal tooth discoloration is usually caused by tooth decay or certain health conditions. Discolored teeth that naturally occur can't be removed just by brushing your teeth diligently. Even toothpaste that has claims to whiten teeth may not be able to successfully whiten your teeth again. It's the same with whitening ingredient claims that many people believe can whiten teeth naturally. Unfortunately, there are still many who are consumed by these claims without knowing the side effects that might actually damage their teeth.

Quoting a discussion from the American Dental Association, here are some examples of myths and facts about natural ingredients that people often use as teeth whitening ingredients.

1. Fruits
   1. Myth: many recommend that sour fruits or processed sour fruits can be used to whiten teeth, for example oranges, lemons, apple cider vinegar. The same goes for fruits that contain digestive enzymes such as pineapple and mango.
   2. Fact: fruits do contain abundant vitamins which are very good for the body. But, fruits that contain a lot of acid are actually not good if you eat them too often or rub them on your teeth because the acid in these fruits will actually erode and damage your tooth enamel.
2. Baking Soda
   1. Myth: brushing your teeth with a mixture of baking soda and water can remove stains on your teeth.
   2. Fact: just like the acid content in fruits, baking soda also has abrasive properties that can erode the layers of your teeth and make your teeth sensitive.
3. Charcoal or Charcoal Powder
   1. Myth: Many toothpastes contain charcoal powder that claims to whiten teeth. Brushing your teeth with charcoal powder is also believed to remove tooth stains.
   2. Fact: There is no evidence that brushing your teeth with charcoal powder can help whiten your teeth. Charcoal powder is also an abrasive just like acid and baking soda. The more eroded your tooth enamel is, the more visible the layer under the tooth enamel or dentin will actually make your teeth look more yellow because the dentin layer itself is yellow.
4. Spices and Oils
   1. Myth: Gargling with coconut oil or using spices is believed to whiten teeth.
   2. Fact: there is no evidence to show that oils and herbs work as teeth whiteners. Better you use oil and spices to prepare healthy food.

So, from the discussion above, what should be done to overcome the problem of yellow teeth? Come on, read the following article about Tips for Safe and Correct Teeth Whitening.

Ref.: https://www.mouthhealthy.org/all-topics-a-z/natural-teeth-whitening/