INTRODUCTION
It is well known that regions of human skin exposed to the environment can incur significant damage due to sun, wind, and indoor and outdoor pollutants. The pathological effects of skin exposure to sunlight have been studied extensively and are well documented.1-3 In general, the areas most exposed to the environment are the skin of the face and neck. These regions are much less protected by clothing compared to skin on other exposed parts of the body.4 In addition to being more vulnerable to environmental insults and oxidative stress, skin on the neck is thinner and especially prone to signs of aging due to the biomechanical properties of repetitive movement and extensibility, which increases its susceptibility to wrinkles and sagging. The presence of fewer sebaceous glands, especially in women, as well as less collagen and subcutaneous fat leads to less oil production, less moisture, loss of volume, and increased skin laxity.4,5 Further, the neck region is often neglected in terms of a lack of application of moisturizer and sunscreen.5
In addition to environmental insults at the surface of the skin, internal cellular processes are associated with aging that lead to diminished levels of nitric oxide (NO) within the skin.6-8 NO plays a vital role in maintaining homeostasis in the skin by increasing microvascular delivery of nutrients and oxygen to cells, including fibroblasts, and NO contributes to maintenance of the protective barrier function of skin as well as wound healing and tissue regeneration.7,9-13 The extensive microcirculatory system is located next to the reticular dermis within the dermis layer.14-16
