| IntroductionIn recent years, ultraviolet radiation reaching the earth' s surface has been increasing constantly because of the damage of ozonosphere. Long - term and excessive ultraviolet expousure will induce skin cancer and the acceleration of skin aging, etc. As one of those hurts, skin aging catches our attention more and more.However, present non - wound methods of evaluating skin aging have some limitations. Some are influenced by doctors 'subjective opinions, so they are difficult to quantify. Other methods are not applicable to large sample because of much losing information, complicated operation and expending too much time etc. Furthermore, there are obvious errors in those methods, as people usually substitute the ambient UV intensity for the individual UV exposure.In this study, we adopt non - wound method digital image technology to collect information of skin morphologic data and use image analysis software, in combination with the investigation of general condition and UV exposure history, to study the quantitative evaluation method for skin aging of the dorsal hands. It may open out the influence of age and UV exposure to skin aging and introduce a objective method of evaluating skin aging. It is also significant to evaluating the fatalness of the depletion of the ozonosphere and effects of skin cosmetology.Objects and methodsWe adopted the method of cluster sampling. The whole people in one village were chosen from Yacheng area in Sanya city, Hainan province. General condition, health status and outdoors time in major -stage life of subjects were collected by questionnaires. With the normative method, the digital photo of each subjects dorsal hand was got by digital camera (Sony DSC -F828) with high resolving power. Combining with the results of questionnaires and the percentage of sunny days in local area, the individual UV exposure time was calculated.After the clean of questionnaires and digital photos, 453 subjects who did not have skin hypersensitivity, cosmetic using and skin diseases on hands were chosen.All photos were grouped by age. 20% subjects were randomly selected as sub —sample. The software "Image —Pro Plus 5.0" was adopted to analyze the photos of sub - sample to filter skin indexes primarily. Then, we measured the primary skin indexes of all subjects and classified the individual skin aging level with the Beagley — Gibson hand aging classification criterion.By the use of the software SPSS 12. 0, we adopted bivariate correlations, ANOVA, multinomial linear regression, etc to analyze the relationship between skin texture indexes and individual UV exposure time, age and so on. We also studied the relationship of skin texture indexes and aging level classified by Beagley - Gibson hand aging classification criterion to explore a objective and quantitative method to evaluate skin aging.Results1. In the low and the high UV exposure population, the average skin aging level was 2.47 and 3. 81 separately and the percentage of aging was 13. 8 and 54. 4 separately. In general, the level and the percentage of aging in the low UVexposure group were both significantly lower than the high UV exposure group ( P < 0.05). At 40 years old, there were more than 50% subjects whose aging level of hand skin were higher than M. In high UV exposure population skin aging appeared 10 years earlier than that in low UV exposure population.2. By analyzing the photos of sub - sample, it was found that the related indexes of block numbers, angles and the distances between adjacent wrinkles could reflect the degree of skin aging.3. After all subjects were involved, it was found that all the indexes were correlated with the age and UV exposure time except the minimal angle. In the related indexes, the maximal standardized distances between adjacent wrinkles, the difference between the maximal standardized distances and the minimal standardized distances, the average of 10 times standardized distances, block numbers, the average of angle numbers, the maximal angle and the margin between the maximal angle and the minimal angle had a stronger correlation with the age and UV exposure.4. Influence factors of the indexes(1) The means of the distances between adjacent wrinkles ( Y,) was influenced by UV exposure time ( X,) , age ( X2) and obesity extent ( X3). Regression equation;Y, = 10. 5477 +0. 3047 X, +0. 1017 X2 -0.1514 X3. And when other factors were fixed, the value of the space increased with the increasing of UV exposure time and age, and decreased with the increasing of obesity extent.(2) The average number of blocks ( Y2) was influenced by UV exposure time ( Xj) , age ( X2) , gender ( X3) , obesity extent ( X4 ) and smoke ( X5). Regression equation;Y2 =32.7321 -0.5492 X! -0.1469 X2 -3.4181 X3 +0. 425 X4 + 3. 6793 X5. When other factors were fixed, the average number of blocks decreased with the increasing of age and individual UV exposure time, and increased with the increasing obesity extent. The average number of blocks was more in male than in female, more in smokers than in non — smokers.(3) The average of angle numbers (Y3) was influenced by UV exposure time ( X,) , age ( X2) , gender ( X3) and obesity extent ( X4). Regression e-quation;Y3 =5. 2385 -0. 0398 X, -0. 0078 X2 -0. 347 X3 +0. 0232 X4. It decreased with the increasing of UV exposure time and age, while increased withthe increasing of obesity extent . And the average of angle numbers in male was less than in female.(4) The maximal angle (Y4) and the difference between the maximal angle and the minimal angle ( Y5) were both influenced by UV exposure time (XL) , gender (X2) and obesity extent (X3). Regression equation;Y4 =142. 8279+2.2307 X, +8.4878 X2 -1.06 X3iY5 =112.7424 + 1.9832 X, +7. 0216 X2 -0. 8032 X3. They increased with the increasing of exposure time, decreased with the increasing of obesity extent . And these indexes in male were larger than in female.As the distances between adjacent wrinkles and the average number of blocks of skin texture were concerned, the major influence came from age among all factors. To the average of angle numbers, the influence of individual UV exposure time was similar to age. The individual UV exposure time influenced the largest angle and the difference of angle most.5. With the increasing of skin aging level of hand the average number of blocks and the average of angle numbers decreased in Hainan population, however, the maximal angle and the difference of angle increased generally. With the increasing of skin aging level of hand, the 10 times standardized distances between adjacent wrinkles increased, and 95% C. I. of it in every skin aging level were independent with each other. Among the aging level 1 to 2, 3 to 4, and 5 to 6, block numbers and average of angle numbers could distinguish the different aging level clearly. Among the aging level 1 to 2 and 3 to 4, the largest angle and the average of angle numbers could distinguish them.Conclusion1. With the increasing of age and individual UV exposure time, the distances between adjacent wrinkles, the number of blocks, the number of angles and the value of angle increased or decreased, and they could reflect the extent of skin aging objectively.2. Maybe the maximal angle and the difference between the maximal angle and the minimal angle are the characteristic changes, which could distinguishskin photoaging from natural aging. The distances between adjacent wrinkles and the number of blocks mainly reflect skin natural aging.3. The method we adopted to evaluating the skin aging could quantify the skin aging and describe the skin aging in details.
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