The hair follicle is one of a few human tissues
containing stem cells. The stem cells are interspersed
within the basal layer of the outer root sheath
and in an area called the bulge. From this reservoir
stem cells migrate to hair matrix and start to divide
and differentiate. Their behavior is controlled
by numerous cytokines produced by cells of the dermal
papilla. Dermal papilla cells and some cells of
the inner and outer sheaths of the follicle from
androgen-dependent hairs have androgen receptors
in their cytoplasm and nucleus. Androgens indirectly
control hair growth by influencing the synthesis
and release of cytokines from the dermal papilla
cells.
Cosmetic ingredients affecting hair growth
belong to one of the following groups: cell stimulating
ingredients, antiandrogens and materials acting
on potassium channels. Further development of
active ingredients selective for certain steps
in the process of hair growth will enable more
successful therapy of hair growth disorders.
