Dear Valerie: Is it possible to selectively reform broken disulfide bonds without significantly reacting with other amino acids? 

—Broken, Not Bowed

Dear Broken:

Your question implies that broken disulfide bonds can be reformed as they were, and the reality is, they can’t. In hair, once a disulfide bond breaks, it doesn’t hang out; it’s oxidized pretty quickly to a sulfonic acid group. This is irreversible. The only time a broken disulfide can be somewhat reformed is by reduction of the cystine to a thiol via a reducing agent, then is reformed through oxidation (think perm). This is not a selective process and doesn’t reform quite the same. 

Valerie George is a cosmetic chemist, science communicator, educator, leader, and avid proponent of transparency in the beauty industry. She works on the latest research in hair color and hair care at her company, Simply Formulas, and is the co-host of The Beauty Brains podcast. You can find her on Instagram at @cosmetic_chemist or showcasing her favorite ingredients to small brands and home formulators at simply-ingredients.com.