Is eating one lemon a day really bad for your teeth?

Acid erosion: Lemon are very acidic and acids will erode your teeth. So eating lemons or sucking on them will erode you teeth. Once the enamel is gone it will not come back. So beware of lemons and any other food that is acidic.

Eating or sucking?: I have personally witnessed the damage caused by sucking on lemons. The lemon causes erosion on the backside of the upper front teeth, when they are sucked for extended periods. Lemons contain citric acid (5-6%) which gives it a sour taste. I would remain cautious, especially if you grind your teeth or have recession.

Sucking on lemons: Really bad? It's relative to alternatives and extent of time you do it for. I would refrain from sucking on lemons altogether. Using the juice of a lemon in food is fine. In liquids it would be ok if you just drink the liquid but not if you sip on it for an extended time.