What is the common effect of using too much heat on hair?

Using too much heat on hair leads to reduced moisture levels within the hair strands. Hair is composed of proteins, primarily keratin, and excessive heat application can cause the cuticle—the outer protective layer of the hair—to become damaged. When this happens, the hair loses its ability to retain moisture, resulting in dry, brittle strands that may be prone to breakage and split ends. This loss of moisture is detrimental because hydrated hair is essential for maintaining elasticity, shine, and overall health.

The other options do not align with the effects of excessive heat. While using heat tools might temporarily increase shine or improve manageability, these are short-term effects that are often accompanied by long-term damage, including moisture loss. Strengthening of hair does not occur as a result of heat exposure; rather, the protein structure can weaken over time with repeated high temperatures. Thus, excessive heat usage primarily manifests as a significant reduction in moisture, making the correct answer a direct reflection of the consistent damage caused by improper heat application.