A study on neck skin physiology and its application to development of cosmetics

The neck is a sun-exposed area. It seems to show the symptoms of photo-ageing as well as facial skin in the elderly. However, the physiological study of neck skin has hardly been reported. We examined the change of skin physiological properties at a neck site with ageing for 61 women (18—69 years old) compared with a cheek site. Water content in stratum corneum (SC) was higher, transepidermal water loss (TEWL) was lower and the turnover rate of SC judged from corneocyte area was slower at the neck site compared with the cheek site. Skin thickness was thinner, skin extensibility and elasticity were higher, skin grooves were deeper, and anisotropy of skin furrows was lower at the neck site than those at the cheek site. It was shown that the neck was also affected by sunlight but not so much as the cheek from the result of gelatinase activity detected in the tape stripped SC. Skin elasticity decreased with ageing at the neck site as well as the cheek site. Fine wrinkles were remarkably increased in the direction of Langer's line with ageing at the neck. Most skin physiological parameters at the neck showed the value between the cheek (heavily sun-exposed area) and back (not sun-exposed area). From these results, it was considered that not only intrinsic ageing but also photo-ageing affected the neck skin. We developed the prototype of cosmetics corresponding to neck skin physiology based on these results, and evaluated the effectiveness of the prototype product by a consumer test including skin measurement for 4 weeks. After treatment, water content increased, and it gave satisfaction in the skin colour brightness, skin elasticity and skin texture improvements for almost all volunteers. It was concluded that the prototype product was useful in neck skin treatment.