From Longman Dictionary of Contemporary Englishsomething is only skin deepsomething is only skin deepused to say that something may seem to be important or effective, but it really is not because it only affects the way things appear Beauty is only skin deep. → skin
Examples from the Corpus
something is only skin deep• But, as in life, beauty is only skin deep.• Beauty is only skin deep, as they say, but I would have hoped for a lot more from a C64. 