Some people straighten their head-hair with what's named:

• Keratin straightening
• Keratin smoothening
• Keratin rebonding
• Keratin treatment

It is an external hair straightening procedure in which an allegedly Keratin containing thick solution is smeared on the hair, then heated with an iron bar to change the texture of the hair; it is often considered a risky procedure both to a customer and a provider, in between other reason, due to breathing formaldehyde gas which is typically produced through the heating.

If, indeed, Keratin alone, can make human hair straighter, is it biologically sensical to assume that at least in some rare cases of Keratin insufficiency (?), Keratin supplements and/or Biotin supplements (I understood that Biotin plays a role in biosynthesis of Keratin) could make a person's hair straighter?