Cosmetic & Laser Surgery Institute | Ultraviolet Radiation
Led by Dr. Diana Parnell, dermatology practice located in Marin County, CA offering the latest in medical and cosmetic dermatology
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Ultraviolet Radiation

UV solar radiation (UVR) causes premalignant lesions known as actinic (solar) keratoses as well as 90% of all skin cancers, especially basal cell carcinoma, squamous cell carcinoma, and malignant melanoma. It also causes sunburns, photoaging, alters DNA, and suppresses the immune system. It is the main cause of cataracts.

There are three types of UVR but only two that currently concern us:


UVB causes most sunburns, synthesizes vitamin D and results in delayed tanning. UVB is prevalent only when the sun is high in the sky – between 10 AM and 4 PM. UVB exposure increases 8-10% for every 1000 feet above sea level, so it is very important to use protection at higher elevations. Since snow reflects up to 80% of UV, it nearly doubles the exposure.


UVA rays are long wavelengths that penetrate window glass and travel more deeply into the skin. They constitute more than 90% of all ultraviolet rays. UVA is present in the same amount all day long, all year long and is independent of altitude, atmospheric or weather conditions. It bears major responsibility for aging of the skin, most skin cancers including malignant melanoma, and suppression of the immune system. About 50% of UVA exposure occurs in the shade.

Important Statistics

One in five Americans will get skin cancer in his/her lifetime. Actinic keratoses (premalignant lesions) are the most common lesions caused by the sun followed by basal cell carcinoma and squamous cell carcinoma each being well over 1 million cases annually. Basal cell carcinoma is the most prevalent skin cancer in young and middle-aged adults, however squamous cell has overtaken it in elderly patients who have an extensive sun exposure over their lifetime. The incidence of malignant melanoma has markedly increased over the last 30-40 years. A study of 1621 Australians found that regular use of sunscreens reduced the risk of malignant melanoma by 50-73%. In the US, people sitting on the left side of the car receive approximately 6 times the dose of UV radiation on the left side of the head, neck, arm and hand as compared to the right side. As would be expected there are more basal cell, squamous cell and melanoma skin cancers on the left side of the face and left arm due to driving. This can be lessened by regular sunscreen use.

Tips to Protect Yourself

While UVR peaks in the summer, more than half the annual total is emitted during the rest of the year. Basic, daily, year-round, sustained protection is the key. There is no such thing as a healthy tan. Tanning is the skin’s response to DNA cellular damage.

To learn more about the services we offer or to schedule an appointment, contact The Cosmetic & Laser Surgery Institute today!