Hi, in this part, we'll discuss interaction between skin and the environment, and we'll discuss such environment points like ultraviolet radiation, temperature, humidity or contact skin with some plants, for example, and direction between plants, skin, and ultraviolet radiation, and the first part, and I think that's the most important part of environment which acts on the on the skin of the human being is ultraviolet radiation. The solar spectrum contains a lot of different rays. Between them are rays of visible light, infrared rays, and ultraviolet rays. There are rays of visible light are between 400-700 nanometers. Infrared light waves are between 900 and more nanometers, and ultraviolet rays consist of three different rays; ultraviolet rays A, B, C, and ultraviolet C waves are between 100-290 nanometers. Ultraviolet B between 290-320 nanometers, and ultraviolet A between 320-400 nanometers. It's very important, and they have different waves because they could take different pattern in solar spectra, and at the same times, it could penetrate the atmosphere, and our skin on the different deep, and so ultraviolet C could reach only the ozone layer of the Earth, and they can't go through the ozone layer, and only in some parts of the Earth like Australian, for example, they could reach the surface of the Earth which around it'll be into ultraviolet A radiation can reach skin surface, and ultraviolet A radiation is less energetic than ultraviolet B but at the same time they could penetrate skin to the level of dermis but ultraviolet B rays only the level of epidermis, and ultraviolet spectrum which reach our skin contains on 95 percent of ultraviolet A, and only 5 percent of this rays are ultraviolet B rays, and they have different action in the skin which ultraviolet B leads to the pigmentation process. They activate melanocytes basal layer of the skin, and at the same time they damage cells, especially keratinocytes. That's why they could lead to the reaction like carcinogenesis in the future, and when we say about skin tanning, it is the action of ultraviolet B rays. That's why we must understand three different time for realization of action of this ray on the skin. The first is a sunburn or immediate redness of the skin. It lasts some hours after sun exposure, and it leads to redness, and to some sensation of burning of the skin, if a sun exposure was very high. The next one is action due to some cell damage in the deep layer of the epidermis. It starts in some weeks after the sun overexposure, and it leads to dryness of the skin to some xerotic skin, and sometimes to hyper xerotic skin, and patients in this period must use emolients, must use cream [inaudible] , for example, to prevent the damage, and to prevent the dryness of the skin. The third part of this action will be in some years, sometimes, some decades after the burning of the skin with ultraviolet B rays, and it is characterized by some process like actinic keratosis, like development of skin cancer, for example, BCC or squamous cell carcinoma, and in some patients, it results also in development of melanoma because ultraviolet B rays acts on the melanocytes also. Ultraviolet A rays are longer than ultraviolet B rays, and then penetrate skin to the deeper layer than ultraviolet B. They penetrate skin to the level of dermis, and in dermis they could accumulate their action on the fibroblast, and they actually lead to the changes in their activity, and in their collagen, and elastin fibers, and during some years, these changes will lead to the process like wrinkling, atrophy of the skin. That's why ultraviolet B radiation is very important for the development of skin aging due to photo damage. Another part of solar spectrum, infrared radiation. They are have a long wavelength, more than 800 nanometers to one millimeter perhaps, and they penetrate skin deeper than ultraviolet radiations. They penetrate skin to the level of subcutaneous tissue, and here they lead to some activity in the vessels and some sensation of heat but the action of infrared radiation on the skin is most like the action of ultraviolet radiation, and they could also give some changes in cells, and proteins, and lipids, that's why infrared radiation have not only benefits, but also harmful aspects in their action. Sometimes infrared radiation using therapy of some disease, and sometimes you must protect skin from infrared radiation, and in some photo protections creams, we can see that they contain some special components against infrared radiation, and such components are tocopherol, for example, antioxidants. One of these antioxidants, tocopherol, is the most active against infrared radiation but not just only against after infrared radiation but against their problem which after infrared radiation active action of the skin. Also, visible light is a part of the solar spectrum, and visible light is also very important to skin changes, and some of those who walk during the whole day with one part of his face, for example, to the window, and another part to the shade, we will have some changes in this part of skin, and the skin where there was the action of visible light will change action of ultraviolet B, for example, like ultraviolet A rays, and the visible part of solar spectrum also plays an important role for this process, and ultraviolet infrared radiation, visible light, all are the part of solar activity, and when we discuss some problems with our skin due to action of environment, the solar spectrum is the most important part in this discussion.
