Stay protected!
Article excerpts by Heather Brannon, M.D.
Sunlight has a profound effect on the skin causing premature skin aging, skin cancer, and a host of skin changes. Exposure to ultraviolet light, UVA or UVB, from sunlight accounts for 90% of the symptoms of premature skin aging. Many skin changes that were commonly believed to be due to aging, such as easy bruising, are actually a result of prolonged exposure to UV radiation.
What is UV Radiation?
The sun gives off ultraviolet radiation that we divide into categories based on the wavelength.
- UVC – 100 to 290 nm
- UVB – 290 to 320 nm
- UVA – 320 to 400 nm
UVC Radiation
UVC radiation is 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 outer layer of skin, the epidermis, and is the primary agent responsible for sunburns. It is the most intense between the hours of 10:00 am and 2:00 pm when the sunlight is brightest. It is also more intense in the summer months accounting for 70% of a person’s yearly UVB dose. UVB does not penetrate glass.
UVA Radiation
UVA was once thought to have a minor effect on skin damage, but now studies are showing that UVA is a major contributor to skin damage. UVA penetrates deeper into the skin and works more efficiently. The intensity of UVA radiation is more constant than UVB without the variations during the day and throughout the year. UVA is also not filtered by glass.
Damaging Effects of UVA and UVB
Both UVA and UVB radiation can cause skin damage including wrinkles, lowered immunity against infection, aging skin disorders, and cancer. However, we still do not fully understand the process. Some of the 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, 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.
Immune System Effects
The 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 prevent this cell death allowing cells to continue to divide and possibly become cancerous.
Skin Cancer Caused by the Sun
The ability of the sun to cause skin cancer is a well-known fact. The 3 main skin cancers are melanoma, basal cell carcinoma, and squamous cell carcinoma. Melanoma is the most deadly skin cancer because it metastasizes more readily than the other skin cancers. It is believed that the amount of exposure of the skin to the sun before the age of 20 is actually the determining risk factor for melanoma. Basal cell carcinoma is the most common skin cancer and tends to spread locally, not metastasize. Squamous cell carcinoma is the second most common skin cancer, and it can metastasize although not as commonly as melanoma. The risk of getting basal cell carcinoma or squamous cell carcinoma is determined by a person’s lifetime exposure to UV radiation and the person’s pigment protection.
LESSON: Wear your SUNSCREEN
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