The Pilosebaceous Unit

If you have not done the EPIDERMIS and the DERMIS section, please do so before you do this section.

Key concept

The hair follicle and sebaceous gland develop together as a unit, the pilosebaceous unit, from a collaborative interaction between the epidermis and dermis. The result is a downward growth of keratinocytes into the dermis. Important parts of the hair follicle, the dermal papilla and the follicular sheath, are derived from the mesenchyme.

Bullet Summary

• Week 12: Condensations of mesenchyme
• Week 14: Early hair peg
• Week 16: Canalization of the hair peg
• Week 18: Bulbous hair peg
• Week 18-26: Melanocytes migrate into the hair bulb

Introduction

Primary hair follicles are the first to appear. They are spaced at regular intervals on the face and scalp. Follicle development is not synchronous. Generally development proceeds in a cephalocaudal direction. Thus, the timing of the developmental stages is subject to considerable regional variation.

To study the pilosebaceous unit over time click on one of the buttons below:

Week 12
Week 14
Week 16
Weeks 18
Weeks 26