Irregularity skin index (ISI): a tool to evaluate skin surface texture

Background/aims: Irregularity of skin surface microtopography is difficult to evaluate in Euclidean geometry. Using a fast Fourier transform (FFT), it is possible to convert a space field into a frequency field and to obtain quantitative evaluation of this important feature of the skin. The aim of the present study was to test the applicability of a new parameter, derived from computer assisted FFT, to skin texture, in order to quantify its irregularity. This parameter has the additional advantage of being anisotropic.
Method: The study was conducted on 50 female volunteers. Skin replicas were performed on a healthy area that was not chronically photo-exposed. A new parameter, called "irregularity skin index" (ISI), was identified from FFT. The correlation with volunteers' age was calculated.
Results: ISI was calculated by FFT in two different directions (referred to the x and y axis of the diagram of the FFT and named, respectively, ISIωx and ISIωy). The irregularity skin indexes increased with age of the subjects, showing a correlation with age of r =0.47 (ISIωx) and r =0.51 (ISIωy).
Conclusion: By showing a relatively good correlation with age, ISI seems to be a promising parameter for the study of ageing skin.