How does temperature affect the curling of hair?

Heat plays a significant role in the temporary restructuring of hair. When heat is applied to hair, such as during the curling process, it breaks the disulfide bonds in the hair proteins. Once these bonds are broken, the hair can be re-shaped into curls. As the hair cools, these new shapes are ‘set’ into place, often allowing the curls to hold longer. This is why heated tools like curling irons are effective for creating curls that last, as the heat essentially allows the hair to adopt a temporary new form before cooling down and locking that shape in.

In contrast to this, while humidity can affect the curl’s longevity and how well it holds, it is not the primary determinant in how curls are formed. Other options regarding temperature, such as the idea that cold temperatures make curls tighter, does not accurately represent how hair behaves with temperature changes.