<P> Attached to the follicle is a tiny bundle of muscle fiber called the arrector pili . This muscle is responsible for causing the follicle lissis to become more perpendicular to the surface of the skin, and causing the follicle to protrude slightly above the surrounding skin (piloerection) and a pore encased with skin oil . This process results in goose bumps (or goose flesh). </P> <P> Also attached to the follicle is a sebaceous gland, which produces the oily or waxy substance sebum . The higher the density of the hair, the more sebaceous glands that are found . </P> <P> In utero, the epithelium and underlying mesenchyme interact to form hair follicles . </P> <P> Hair grows in cycles of various phases: anagen is the growth phase; catagen is the involuting or regressing phase; and telogen, the resting or quiescent phase (names derived using the Greek prefixes ana -, kata -, and telos - meaning up, down, and end respectively). Each phase has several morphologically and histologically distinguishable sub-phases . Prior to the start of cycling is a phase of follicular morphogenesis (formation of the follicle). There is also a shedding phase, or exogen, that is independent of anagen and telogen in which one or several hairs that might arise from a single follicle exits . Normally up to 90% of the hair follicles are in anagen phase, while 10--14% are in telogen and 1--2% in catagen . The cycle's length varies on different parts of the body . For eyebrows, the cycle is completed in around 4 months, while it takes the scalp 3--4 years to finish; this is the reason eyebrow hair have a much shorter length limit compared to hair on the head . Growth cycles are controlled by a chemical signal like epidermal growth factor . DLX3 is a crucial regulator of hair follicle differentiation and cycling . Specifically, colocalization of phosphorylated Smad1 / 5 / 8 complex and DLX3 regulate role for BMP signaling to Dlx3 during hair morphogenesis in animal models . </P>

Where is the root of the hair located