The earliest event in follicular production is the interaction between the embryological ectoderm and the mesoderm. During the second month of pregnancy of pregnancy, development is from the epidermal thickenings, called placodes. Molecular signaling signals the mesenchyme thus, the overlying epidermis sends molecular signals back which induces of the mesenchyme. This action is complex and occurs throughout the follicular metamorphosis. These embryological are described below.
Stage of Pregerm:
The superficial of the dermis and the simultaneous thickening of basal epidermal cells occurs almost immediately , and the first sign of a follicle is apparent.
Stage of the Germ:
The “hair germ” cells begin o replicate at the same time the underlying mesochymal cells form, which will become the dermal papilla. At this point, the basal epidermal cells becomes elongated.
Stage of the Hair Peg:
The hair peg stage forms a downward column that seems to propel the mesochymal aggregate downward.
Stage of Bulbous-Peg:
Three areas of swelling will appear juxtapose to the peg and extends downward. Superiorly, swelling will form the apocrine gland. The middle swelling forms the sebeaeous gland, while the lowest bulb forms the arrector pili attaches to the muscle. Near the sebaceous gland, forms an independent hair follicle. Epidermal cells during this stage at the advancing base of this column and a portion of the underlying mesodermal cells forms the dermal papilla.
Stage of Primordial Hair:
The dermal papilla begins to actively proliferate by forming the early matrix and this is the initial hair shaft that moves upward. The central cells of follicular peg degenerate and the emerging hair seems to push out the plug so a hair canal can be formed. The development of hair theoretically begins at nine weeks and by twenty two weeks the entire initial population of follicles is complete.
Including those on a scalp. It is estimated that five million follicles cover the human body at birth with approximately one hundred thousand being an infant’s scalp. It is estimated also that no new hair follicles develop post birth.
At birth our less synchronized shedding by the third or fourth after birth. This synchronization with a decreased successive population of hairs and by year one, all follicles are in stages of growth cycle, which we discuss in further blogs .