Hair 101: How Hair Reacts Under Different Conditions

We’ve established that hair is made up of mostly protein, and that it requires moisture to maintain elasticity. We also know about the hair growth cycle and the rate at which hair grows. In this post, we’ll learn how hair reacts under different conditions.

Temperature: Hot or Cold

When you apply heat to your hair, some of the hydrogen bonds between the keratin fibres are broken. This temporarily loosens the curl pattern of the hair. Hair can be straightened by applying direct heat e.g. using a flat iron, or by applying indirect heat e.g. using a hair dryer on hair that is under tension. The curl pattern can be “reset” by wetting the hair.

Indirect heat (e.g. warm water or a hair dryer) not only loosens the curl pattern, it also opens the cuticle. An open cuticle allows the hair to absorb whatever is applied to it. On the other hand, the cuticle closes when hair is cooled e.g. rinsing with cold water or using the cool shot button on a hair dryer. Thus, when you want your hair to absorb something, indirect heat helps (e.g. sitting under a hair dryer when you deep condition your hair). When you want the hair to retain what it has absorbed, cool it down.