“Beauty is only skin deep, but ugly goes clean to the bone.”

Source: Romancing Mister Bridgerton

From interview with Komal Nahta

"The Triumph of Assurance", Orthodox Paradoxes, Or, A Believer Clearing Truth by Seeming Contradictions (1647), p. 41. Compare: "Many a dangerous temptation comes to us in fine gay colours that are but skin-deep", Mathew Henry, Commentaries. Genesis iii.

"Mirror, Mirror on the Wall, I Don't Want to Hear One Word Out of You"
The Snake Has All the Lines (1960)

Introductio ad prudentiam: Part II (1727), Gnomologia (1732)

The sad truth is that attractive people do better in school, where they receive more help, better grades, and less punishment; at work, where they are rewarded with higher pay, more prestigious jobs, and faster promotions; in finding mates, where they tend to be in control of the relationships and make most of the decisions; and among total strangers, who assume them to be interesting, honest, virtuous, and successful. After all, in fairy tales, the first stories most of us hear, the heroes are handsome, the heroines are beautiful, and the wicked sots are ugly. Children learn implicitly that good people are beautiful and bad people are ugly, and society restates that message in many subtle ways as they grow older. So perhaps it’s not surprising that handsome cadets at West Point achieve a higher rank by the time they graduate, or that a judge is more likely to give an attractive criminal a shorter sentence.
Source: A Natural History of the Senses (1990), Chapter 5 “Vision” (pp. 271-272)

Second Week, Fourth Day, Book iv. Compare: "Bone and Skin, two millers thin, Would starve us all, or near it; But be it known to Skin and Bone That Flesh and Blood can’t bear it", John Byrom, Epigram on Two Monopolists.
La Seconde Semaine (1584)

Epigram on Two Monopolists as quoted in Bartlett's Familiar Quotations, 10th ed. (1919)

Source: Small Great Things