What is a contraindication for using chemical hair straighteners?

Using chemical hair straighteners on chemically treated hair is a contraindication because the hair is already compromised and may not withstand additional chemical processing. When hair has undergone previous chemical treatments, such as relaxing, perming, or other coloring processes, it is often more fragile and susceptible to damage. Introducing more chemicals can lead to breakage, excessive dryness, or scalp irritation.

This is particularly important to consider, as the overlapping of different chemicals can create unpredictable reactions, leading to severe structural damage to the hair. The integrity of the hair needs to be carefully assessed to avoid causing harm.

In contrast, while an oily scalp or weather conditions might affect the application process or results, they don't pose the same level of risk to the hair's health as combining a chemical straightener with already chemically treated hair. Similarly, colored hair might still be eligible for treatment under certain conditions, but with careful evaluation.