The sun gives off UV Radiation and are divided into three categories based on their wavelengths:
UVC - 100 to 290 nm
UVB - 290 to 320 nm
UVA - 320 to 400 nm
UVC Radiation
UVCradiationis almost completely absorbed by the ozone layer and does not affect the skin. UVC radiation can be found in artificial sources such as mercury arc lamps and germicidal lamps.
UVB Radiation
UVB affects the epidermis, or outer layer of the skin, and is the primary agent responsible for sunburns. This radiation is most intense from 10:00 am and 2:00 pm when the light is the brightest.
UVA Radiation
UVA is a major contributor to skin damage which penetrates deeper into the skin. The intensity of UVA radiation is more constant than UVB without variations during the day and throughout the year.
Damaging Effects of UVA and UVB
Both UVA and UVB radiationcan cause skin damage including wrinkles, lower immunity against infection, aging skin disorders, and cancer. Possible mechanisms for UV skin damage are collagen breakdown, the formation of free radicals, interfering with DNA repair, and inhibiting the immune system.
Collagen Breakdown
In the dermis, the inner layer of skin, UV radiation causes collagen to break down at a higher rate than with just chronologic aging. Sunlight damages collagen fibers and causes the accumulation of abnormal elastin. When this sun - induced elastin accumulates, enzymes called metalloproteinases are produced in large quantities. Normally, metalloproteinases remodel sun - injured skin by manufacturing and reforming collagen. However, this process does not always work well and some of the metalloproteinases actually break down collagen. This results in the formation of disorganized collagen fibers known as solar scars. When the skin repeats this imperfect rebuilding process over and over wrinkles develop.
Free Radicals
UV radiation is one of the major creators of free radicals. Free radicals are unstable oxygen molecules that have only one electron instead of two. Electrons are found in pairs, so the molecule must scavenge other molecules for another electron. When the second molecule looses its electron to the first molecule, it must then find another electron, repeating the process. This process can damage cell function and alter genetic material. Free radical damage causes wrinkles by activating the metalloproteinases that break down collagen. They cause cancer by changing the genetic material, RNA and DNA, of the cell.
DNA Repair
UV radiationcan affect enzymes that help repair damaged DNA. Research into the role of specific enzyme called T4 endonuclease 5 (T4N5) has in repairing DNA.
Immune System Effects
Our body has a defense system to attack developing cancer cells. These immune system factors include white blood cells called T lymphocytes and specialized skin cells in the dermis called Langerhans cells. When the skin is exposed to sunlight, certain chemicals are released that suppress these immune factors.
Cell Death
The last line of defense of the immune system is a process called apoptosis. Apoptosis is a process of cell - suicide that kills severely damaged cells so they cannot become cancerous. This cell - suicide is seen when you peel after a sunburn. There are certain factors, including UV exposure, that prevents this cell death allowing cells to continue to divide and possibly become cancerous.
UVC - 100 to 290 nm
