Beauty is only skin deep
Physical beauty is superficial.
Proverb. First found in a work by Sir Thomas Overbury, 1613:
"All the carnall beauty of my wife, Is but skin deep."
What his wife thought isn't recorded. There is a fanciful work attributed to Overbury called A true and historical relation of the poysoning of Sir Thomas Overbury, 1651. Perhaps she had him worried?
'Skin deep' is now also used to allude to anything superficial. An early use of this was also attributed to Overbury in 1613, in Ordinary Fencer Works, 1856:
"His wounds are seldome above skin-deep."
See also: the List of Proverbs.