4. Temperature damage
The application of external heat is essential to some hair treatments, but it can interact with chemicals and damage hair. Like all parts of the body, hair contains water. When styling tools raise the temperature of hair above 212 degrees F, microscopic droplets of water inside the hairs boil and evaporate. This causes the hairs’ surfaces to bubble and crack, resulting in structural damage including flaking, cracking and loss of sheen. Chemicals from treatments are able to penetrate the hairs, contributing to loss of natural moisture, oils and pigments. The situation is worsened by the fact that many chemical perms generate their own heat by chemical reaction. These should always be applied professionally, as they can get hot enough to break hair shafts if used improperly.