Is it true using markers to write on media such as CD's or DVD's damages them?

does anyone know from experience if this is actually true? i read that using a sharpie on dvd or cd will damage them because chemicals on the ink will oxidize the metal on the dvd/cd. I also heard that it was ok to use sharpies on printable dvd's because the white layer protects the writeable part of the media. are these 2 statements true?