We’ve discussed the chemistry behind and hair curl and perms a few times, but I started wondering about some of the less-permanent hair styling options out there. A hair “perm” is so-called because it is permanent: a strong reducing agent reduces the disulfide bonds in the hair, which is then physically straightened and re-oxidated to form new disulfide bonds in a different configuration. In this case, covalent bonds are permanently disrupted. But, what about non-permanent hair styles? Specifically, I was thinking about that middle-school locker room staple, the hair straightener. How does heat affect the bonds in hair?
A quick Google search later, I have my answer. Electronic straighteners work using the same general procedure as perms: bonds within the hair are broken, the hair is physically straightened, and the broken bonds are reformed in the new, straight configuration. The difference lies in which bonds are being affected. Whereas the chemicals used in perms changed covalent bonds, heat styling disrupts noncovalent interactions -hydrogen bonds. Electric straighteners apply heat to break hydrogen bonds in the alpha keratin protein in hair. The hair shaft is ironed flat and held that way by the straightener’s plates for the H-bonds to reform in a”flat” shape, leading to straight hair. However, the nature of hydrogen bonds also causes the effect to be temporary. Hydrogen bonds in your hair interact with water in the air. More moisture cause the hair to reform its original shape as the original hydrogen bonds are restored. This is why heat-styling is easily undone by humidity.
In any case, although the effects of heat-styling might be temporary, prolonged use can be damaging to the hair. Being addicted to the hair straightener can lead to frizz, dryness, and split ends. If only my middle-school self knew about the science behind post-gym locker room primping.
Sources:
http://www.ccmr.cornell.edu/education/ask/index.html?quid=708
http://www.livestrong.com/article/190915-hair-loss-caused-by-heat-straightening/
http://www.ncbi.nlm.nih.gov/pubmed/15037918
Woah… hair…
This is super relevant considering our discussion in class about what happens when you add heat to a system – here, a real life example! 😀
This makes straightening/curling your hair almost seem like a science experiment! It’s strange to think of our irons as hydrogen bond breakers and formers but I guess that’s literally all they’re doing. Thanks for science-ing up my daily routine!