(Concern) How long does teeth whitening last?

I've never had teeth whitening before in my life, but lately I feel the need for teeth whitening.

Teeth whitening is primarily for cosmetic purposes, as it artificially brightens the teeth.

I'm curious about how long the whitening results will last since it doesn't seem to be good for dental health.

If the whitening effect doesn't last long even after the procedure, I wonder if it's not good for my dental health and whether I should do it.ㅠ

I am curious about what kind of care should be taken after teeth whitening and whether there are any foods I should avoid.

I'm really curious about how long the retention period is.