What condition can excessive heat styling cause in hair?

Excessive heat styling can result in heat damage, which is a significant concern for maintaining healthy hair. When hair is subjected to high temperatures from tools such as flat irons, curling wands, or blow dryers, the intense heat can break down the protein structure of the hair shaft. This leads to several visible issues, including brittleness, split ends, and an overall loss of moisture. The altered protein structure makes the hair more susceptible to breakage and frizz, resulting in a compromised hair texture and appearance.

While color fading, oiliness, and dullness can occur for various reasons, they are not specifically the direct result of excessive heat application as heat damage is. Color fading typically results from sun exposure or chemical processes, oiliness is related to the scalp's sebaceous gland activity, and dullness may be associated with buildup or lack of moisture but doesn't encompass the structural damage that heat can inflict. Hence, the primary consequence of applying excessive heat to hair is indeed heat damage.