What characterizes the difference between terminal and vellus hair?

The characteristic that differentiates terminal hair from vellus hair primarily lies in its thickness and pigmentation. Terminal hair is typically thicker, coarser, and more pigmented compared to vellus hair, which is fine, soft, and often colorless or lightly pigmented.

Terminal hair is found in areas such as the scalp, beard, and armpits, where it develops as a result of hormonal changes, particularly during puberty. In contrast, vellus hair is more prevalent in areas of the body that do not require the protective or aesthetic qualities of terminal hair. Understanding this distinction is crucial as it relates to various aspects of hair growth, development, and overall biological function.

While other factors such as growth cycle duration and follicle density may play roles in hair physiology, the most apparent and defining difference between terminal and vellus hair remains their thickness and pigmentation, making this the correct answer.