Instrumental evaluation of antiwrinkle activity of cosmetic products: what's new?

Relation between skin micro-topography, roughness, and skin age

BACKGROUND

The topography of the skin surface consists of lines, wrinkles, and scales. Primary and secondary lines form a network like structure that may be identified as polygons. Skin surface roughness measurements are widely applied in dermatological research and practice but the relation between roughness parameters and their anatomical equivalents are unclear. This study aimed to investigate whether the number of closed polygons (NCP) per measurement field can be used as a reliable parameter to measure skin surface topography. For this purpose, we analysed the relation between skin surface roughness parameters and NCP in different age groups.

METHODS

Images of the volar forearm skin of 38 subjects (14 children, 12 younger, and 12 older adults) were obtained with the VisioScan VC98. The NCP was counted by three independent researchers and selected roughness parameters were measured. Interrater reliability of counting the number of closed polygons and correlations between NCP, roughness parameters, and age were calculated.

RESULTS

The mean NCP/mm² in children was 3.1 (SD 1.1), in younger adults 1.0 (SD 0.7), and in older adults 1.0 (SD 0.9). The interrater reliability was 0.9. A negative correlation of NCP/mm² with age was observed, whereas measured roughness parameters were positively associated with age. NCP/mm² was weakly related to skin roughness.

CONCLUSION

The NCP/mm² is a reproducible parameter for characterizing the skin surface topography. It is proposed as an additional parameter in dermatological research and practice because it represents distinct aspects of the cutaneous profile not covered by established roughness parameters.

The riddle of genuine skin microrelief and wrinkles

Wrinkles result from distinct structural changes occurring in specific parts of the dermis and subcutaneous tissue. There is a need for evidenced-based cosmetology identifying and quantifying the different aspects of wrinkling. Histology allows to detect specific changes associated with particular types of wrinkles. Four main types of wrinkles can thus be recognized, including the atrophic crinkling rhytids, the permanent elastotic creases, the dynamic expression lines, and the gravitational folds. Each type usually develops on specific skin regions exhibiting distinct microanatomical characteristics. Whereas skin microrelief, expression lines and skin folds appear clearly marked at the histological level, only little dermal changes are identified under other reducible or permanent wrinkles compared with the skin immediately adjacent to them. Distinguishing different types of wrinkles brings more precision to the clinical practice. This is of importance because the different types of wrinkles respond differently to cosmetic, dermatological and surgical treatments.

From skin microrelief to wrinkles. An area ripe for investigation

Skin microrelief alters progressively with age. Wrinkles do not result from these changes but are superimposed upon them. Wrinkles result from structural changes in the epidermis, dermis and hypodermis. Four types of wrinkles can be recognized. Type 1 wrinkles are atrophic. Type 2 wrinkles are elastotic. Type 3 wrinkles are expressional. Type 4 wrinkles are gravitational. Each type of wrinkle is characterized by distinct microanatomical changes and each type of wrinkle develops in specific skin regions. Each is likely to respond differently to treatment. Skin microrelief and skin folds can be identified on histological examination. By contrast, only minimal dermal changes are found beneath permanent or reducible wrinkles compared with immediately adjacent skin. A series of objective and non-invasive methods is available to quantify the severity of wrinkling.