How can heat styling tools damage hair?

Heat styling tools can damage hair primarily by causing moisture loss. When hair is exposed to high temperatures from tools such as flat irons, curling wands, and hair dryers, the heat can strip the natural moisture content from the hair shaft. This loss of moisture results in dry, brittle hair that is more prone to breakage. Over time, the cumulative effect of frequent heat styling can weaken the hair strands, leading to split ends and overall damage, including a lackluster appearance.

While the other choices may relate to hair characteristics, they do not directly address how heat leads to damage in the way that moisture loss does. Adding weight to hair, darkening hair color, or changing texture doesn't address the immediate consequences of heat styling. Understanding the effects of heat on moisture is crucial for maintaining healthy hair, especially for those who regularly use styling tools.