There are two major types of hair follicles on the human body which are called terminal hair follicles and vellus hair follicles. Transitioning between terminal and vellus hair follicles occurs during puberty-- vellus hairs in the genital area and axilla are stimulated to become terminal hairs. This transitioning may also occur in disease states such as hirsutism.
Terminal hair follicles
These hairs are larger than vellus hair follicles and extended into the subcutaneous fat tissue (2 -5 mm from the skin surface) during hair growth. These hairs are at least 0.06 mm in diameter. At birth terminal hairs are found on the scalp, eyebrows, eyelashes.
Vellus Hair follicles
The lowest portions of vellus hair extend into the reticular dermis. These hairs are usually less than 0.03 mm in diameter. At birth vellus hairs are most of what is on the body. Abnormal transitioning of vellus hairs to terminal in hirsutism is a classic feature of androgenetic alopecia
These are hairs which have characteristics of both terminal and vellus hairs.