(Concern) Tooth whitening worries..

I didn't realize it when I was wearing a mask due to COVID-19, but now that I live without a mask, I can finally see my yellowish teeth. I had been unaware that my teeth had turned yellow all this time, but now that I take off the mask, it's very noticeable.

I find it hard to just watch my teeth turn yellow, perhaps because I haven't taken good care of my dental health.

I don't smoke, but I always live on coffee, so I wonder if my teeth have turned yellow because of the coffee.

I'm curious about how teeth whitening is performed, whether it can be done in a single session, and if there are any other conditions. Honestly, I want to know everything.

I really want to try teeth whitening, so I would love to hear some sincere personal experiences~

Is it true that it's not possible with just one time and it's expensive?

I'm asking because I have a question.