Understanding Uva And Uvb Radiation

The primary cause of most cases of skin cancer is damage from the sun. The sun’s rays contain ultraviolet type A (UVA) rays and ultraviolet type B (UVB) rays, both of which can cause skin cancer. These rays damage the skin and change its cell replication process, causing abnormal cancer cells to grow unchecked.

UVA and UVB Radiation

Sunlight is made up of rays of light of varying wavelengths. Light in the ultraviolet (UV) range of the spectrum can have damaging effects on skin tissue. Indoor tanning also produces UV radiation.

Longer-wavelength UVA rays penetrate through the epidermis to the lower layers of the skin. They cause immediate skin tanning, as well as aging and wrinkling. Although UVA rays were once thought to cause little damage to the skin, they are now known to contribute to the development of skin cancer. Levels of UVA radiation remain constant throughout the day.

Medium-wavelength UVB rays cause skin damage in the skin’s top layers, and are responsible for delayed tanning, aging and wrinkling. UVB radiation also promotes the development of skin cancer. Not all UVB rays reach the earth’s surface as the atmosphere filters out a significant portion of them. UVB radiation levels vary over the course of the day, and are strongest at midday.

How Does UV Light Affect Skin Cells?

The UV radiation that’s absorbed by skin cells causes them to change in several ways. The skin produces more melanin as a protective mechanism against sun exposure; this is what causes skin to appear tanned. However, this process is not always enough to protect skin, particularly fair skin. Sunburn can result, a reflection of cell death from overexposure to sun. Notably, UV rays can pass through cloud cover, meaning that you can be sunburned even on cloudy days.

Along with your skin’s immediate reaction to sunburn, sun damage can accumulate over time. UV damage to connective tissue can cause wrinkling and surface discoloration. After a lifetime of exposure, older people are at high risk for developing skin cancer.

Both constant exposure and intermittent exposure over long periods of time are associated with skin cancer risk.

The Sun and Abnormal Cell Growth

Along with damaging the skin cells themselves, UVA and UVB radiation can damage DNA such as that of the p53 gene that works to control and inhibit cell replication. When these genes undergo UV-induced mutation, abnormal skin cells may grow without being stopped. Clusters of these abnormal skin cells can form cancerous lesions.

Medical scientists don’t fully understand how this process contributes to each type of skin cancer; however, the short-term and long-term dangers of sun exposure to the skin remain clear.

Increased Photosensitivity

Photosensitivity is an increase in the skin’s natural reaction to the sun’s UVA and UVB rays. Certain factors can accelerate the skin’s reaction to the sun. Symptoms can include a skin rash, which may occur rapidly. Agents that can increase photosensitivity include:

  • Diseases of the skin, including psoriasis and rosacea
  • Drugs, such as antibiotics, antifungals and diuretics
  • Topical agents, such as retinoids and fragrances.

Take extra care in the sun when using products that increase photosensitivity.


American Cancer Society. (n.d.). Skin cancer prevention and early detection. Retrieved June 22, 2010, from http://www.cancer.org/docroot/ped/content/ped_7_1_skin_cancer_detection_what_you_can_do.asp

Canadian Centre for Occupational Health and Safety. (2010). Skin cancer and sunlight. Retrieved June 22, 2010, from http://www.ccohs.ca/oshanswers/diseases/skin_cancer.html

Mayo Clinic. (2009). Sunburn. Retrieved June 22, 2010, from http://www.mayoclinic.com/health/sunburn/DS00964

National Science Foundation Polar Programs UV Monitoring Network. (n.d.). Effects of UV radiation on you. Retrieved June 22, 2010, from http://www.biospherical.com/nsf/student/page4.html

The Skin Cancer Foundation. (2010). Understanding UVA and UVB. Retrieved June 22, 2010, from http://www.skincancer.org/understanding-uva-and-uvb.html

The Skin Cancer Foundation. (2010). The skin cancer foundation photosensitivity report. Retrieved June 22, 2010, from http://www.skincancer.org/skin-cancer-foundation-photosensitivity-report.html

World Health Organization. (2010). UV radiation. Retrieved June 22, 2010, from http://www.who.int/uv/faq/whatisuv/en/index.html