**2. The hair follicle sites of resistance to hair pulling out of the skin**

So let us list the histological conditions necessary to keep the clearly visible hair shaft within the skin:


volve rather many hairs in shedding process at any moment and all these features will be interpreted as hair loss. So the hair loss can be partly decreased by the regulatory mechanisms prolonging anagen VI phase and lowering the proportion of F in the telogen phase.

by this moment OS inner layer cells surrounded by the cells of nonkeratinized outer layers of the OS. In such a way, the nongrowing hair is anchored in the skin. Its loss from the skin is postponed after stopping the growth up to the moment when the keratinized companion layer cells will be peeled into the pilary lumen, and the hair will be shed out of the skin perhaps because the intercellular "glue" is destroyed between keratinized cells like between

After some period of anchoring, the new matrix and bulb regenerate and the new hair starts to grow in this follicle. In such species as mice, one follicle in the early postnatal period can produce four generations of hairs all being kept anchored and allowing new hair to grow past them.

So let us list the histological conditions necessary to keep the clearly visible hair shaft within

(1) The hair shaft must not be too thin and short and rare (like on the cheek of a girl), or such underdeveloped hair most probably would be interpreted as hair loss (**Figure 8**).

(2) There must not be extreme local thinnings of hair shafts caused by the short temporary action of mitostatic agents (stress—hydrocortisone, short time ionizing irradiation). Hairs can be easily broken in these thin sites and hair loss will take place

(3) The keratinization of the hair cortex cells must be perfect enough not to allow the hair to break easily especially after these cells leave the skin in the course of hair growth. The defects of the keratin can be caused by the parasitic organisms or genetic mutations or

(4) When the hair grows, its fixation in the F is possible when the correct proportion of IS and

(5) When the hair stops growing, its fixation in the skin for some time is possible only when the IS is not produced and cannot isolate the modified hair cortex cells of the brush-like proximal club-hair end from companion layer cells. Direct contact between the hair brush-like end and keratinized companion cells seems to be the main mechanism of telogen hair temporary fixation in the skin and postponing of the hair shedding. (6) Unlike the events in the "planned" catagen phase where the IS production is stopped and brush-like proximal hair shaft end is produced, the mitostatic agents do not stop IS formation, and nothing like brush-like proximal hair end is formed (merely thinning pointed end) (**Figure 10**). So the hair shedding is not postponed and is not fixed in the

(7) Relatively high proportion of hair F entered into telogen phase at any moment means that the hair will be neither long nor dense. Even postponed shedding will still in-

hair cuticle layers are produced and their interaction takes place.

skin 8 days after any type of mitostatic action in the proper dose.

**2. The hair follicle sites of resistance to hair pulling out of the skin**

peeling cells of the interfollicular epidermis.

the skin:

76 Hair and Scalp Disorders

(**Figure 9**).

the lack of some nutrients.

**Figure 8.** Transverse histological sections of neighbor hair follicles of nude goat supposedly with nude mutation causing underdevelopment of hairs. The left follicle produced very thin hair (H) as well as rather developed hair root inner sheath (I). The right follicle produced only inner sheath (I) and no hair at all. O, well developed outer hair root sheaths. The right one includes some melanocytes producing melanin. Hematoxylin + eosin.

**Figure 9.** Hair dysplasia caused by the local fine-wool sheep skin X-irradiation by subepilation doze (300 sZv). The left and higher hair segment was formed before the irradiation. This segment is followed by one with some disturbance of normal structure (3 days after irradiation) and progressive thinning of the wool fiber. In the course of further growth, the restoration of original hair diameter took place (lower left hair segment).

**Figure 10.** Polarization microscopy picture of the lower end of the sheep hair which appeared as the result of local X-irradiation of the skin by epilation doze (500 sZv). No "club" or brush-like structures could be seen. White "shining" is caused by the capacity of the very dense keratin regular structure to turn the plane of light polarization between two crossed polaroids (dark background) of "NU" Carl Zeiss microscope.

### **Abbreviations**

