My teeth keep getting more yellow even though I brush twice a day. Why won’t they stay white?

oral hygiene can mitigate their staining effects.

Smoking, Vaping, and Nicotine: How They Yellow Teeth Fast
Tobacco use, whether through smoking or vaping, is a leading cause of tooth discoloration. Nicotine and tar in tobacco are both yellowing agents that can penetrate the enamel and stain teeth.
Even nicotine in vaping products, which is colorless, combines with oxygen to turn yellow, contributing to stains. Quitting these habits not only benefits your overall health but also helps maintain whiter teeth.

Are You Brushing Wrong? Technique, Timing, and Overbrushing
Brushing your teeth