Hi Aud, further to the previous answer, they are actually different plants of the same family. In cooking, you can use either depending on taste: Peppermint has a strong powerful mint flavour, and spearmint has a sweet mild mint flavour.

Thank you! :)

All I know is spearmint has a sweeter taste and is used in candy. Peppermint has a harsher taste and is used in breath mints. Hope this helps.