Periodicity in the growth and shedding of hair.

Ten men, with or without alopecia, were observed for a period of between 8 and 14 years using phototrichograms on a precisely located zone on the vertex of the scalp. Among the various parameters observed, we chose the percentage of hairs in telogen as the criterion for assessment of hair shedding. Mathematical analysis of the variations in this telogen percentage was carried out for each individual subject and for the whole group, as represented by the population mean (or the 'average subject'). This analysis demonstrated the existence of overall annual periodicity, manifested by a maximal proportion of telogen hairs at the end of summer and the beginning of autumn. Some subjects also exhibited a periodicity approximately corresponding to two annual peaks. In those subjects with a very low proportion of hairs in telogen, no periodicity was demonstrated. In another group of subjects, it has been shown that the variations in telogen percentage reflect those observed in hair shedding, assessed in a standardized manner. Periodicity of the telogen percentage, and hence of hair fall, is not independent of climatic factors (sunshine hours), and these must be taken into account when assessing the treatment or prevention of hair loss.

Ageing and hair cycles.

The phototrichogram is a non-invasive technique by which, on the same precise area of the scalp, each individual hair may be identified, and its current growth phase established. This technique was used to study the duration of hair cycles in 10 male subjects, balding and non-balding, by observations at monthly intervals over a period of 8-14 years. The accumulated data served to characterize the effects of ageing in these subjects: a reduction in the duration of hair growth and in the diameter of hair shafts, most evident in the thickest hairs, and a prolongation of the interval separating the loss of a hair in telogen and the emergence of a replacement hair in anagen. These various aspects of ageing of scalp hair contribute to its progressive overall impoverishment. They resemble those observed in the course of male-pattern balding, although their development is less marked.

Hair cycle and alopecia.

Male pattern alopecia is the outcome of profound modifications in the duration, succession and frequency of hair cycles. These phenomena were studied by phototrichogram in 10 male subjects, with or without alopecia, over a period of 15 years. Almost 10,000 hair cycles were accounted for, yielding a detailed picture of the alopecia condition: (1) A decrease in the duration of anagen for a certain proportion of hairs, a proportion which increases in size, the more advanced the alopecia; the result of this premature transformation from anagen to telogen is an increase in the rate of hair loss. (2) A parallel decline in hair diameter. (3) Longer latency periods between the fall of a hair and the onset of regrowth, leading to a reduction in the number of hairs present on the scalp surface. The shorter finer hairs are absent more frequently and absent for longer periods and this contributes to the effect of alopecia.

High-protection sunscreen formulation prevents UVB-induced sunburn cell formation.

A human sunburn cell (SBC) count is used to evaluate the reduction in UV-induced skin damage achieved by a highly protective sunscreen formulation containing 3 filters and reflective pigments (sun protection factor 34). Results indicate that, for the same minimal erythema level, SBC counts do not significantly differ between protected and unprotected skin, showing that the very high efficacy demonstrated against actinic erythema also extends to UV-induced skin damage.

Study of the re-oiling process of hair with the replica technique.

Synopsis In the case of individuals with oily hair, the sebum excreted to the scalp surface spreads over the hair during the days following hair washing. The migration of sebum from the roots to the ends of hairs creates a gradient which may be measured by making casts on appropriate materials. An optical reading device enables the assessment of the alterations of the material brilliancy as a function of the sebum presence. The following parameters may be assessed from the recording: length of the cast, surface, height and width of the peak. Thus, different types of oily states may be identified according to: - the number of days after the last shampoo; - the characteristics of sebum (e.g. quantity, viscosity); - the features of hair. The casts reflect the oily state of hair as accurately as if it were assessed with a sensory method. Thus, this technique enables the study and comparison of oily states. It can be used to determine the efficacy of products having an effect on the re-oiling process of hair.