Sun radiation and SPF

Skin Cancer Awareness month is over, but it’s never too late to expand your knowledge about the risks associated with sun exposure and the damaging effects UV rays can have on your skin and eyes. Ultraviolet light from the sun is comprised of three types of radiation – UVA, UVB, and UVC. UVA, UVB and UVC have varied wavelengths which determines how deeply they penetrate your skin. Understanding each type is the first step in protecting yourself against various skin cancers, premature aging, Actinic Keratosis and eye damage.


UVA rays have the longest wavelength of the three and can penetrate deep into the middle layer of skin, also called the dermis. These rays are responsible for premature aging and issues such as increased skin laxity, wrinkles, pigmentation, and leathery skin to name a few. As a coping mechanism against further damage from UVA rays, your skin darkens which results in a tan. Contrary to popular belief, there is no such thing as a safe or healthy tan. Most importantly, UVA rays can cause skin cancers such as basal cell and squamous cell carcinomas. UVA rays account for roughly 95% of all ultraviolet rays that reach the earth’s surface. UVA rays can penetrate through cloud cover as well as windows, so it is important to use sunscreen even on a cloudy day or while in the car.


UVB rays have a shorter wavelength than UVA rays. These rays affect the outermost layer of skin, more commonly referred to as the epidermis. Despite affecting your skin on a more superficial level, long term exposure to UVB rays can cause lasting damage to your skin and eyes including various skin cancers such as basal and squamous cell carcinomas. Additionally, UVB rays are responsible for delayed tanning and sunburns which are among the leading causes of melanoma – the deadliest form of skin cancer. Fortunately, most UVB rays are filtered by the earth’s atmosphere and cannot pass through glass. It is still important to protect yourself by applying at least 1 ounce of broad-spectrum sunscreen 30 minutes before exposure.


UVC rays are the most harmful type of rays despite having the shortest wavelength of the three. Fortunately, UVC rays from the sun are absorbed almost completely by the ozone layer which means that they cannot make it to the surface or penetrate your skin. UVC rays still exist in some indoor lamps such as mercury lamps and some welding torches, which is why special safety equipment for welding is required.

The Importance of sun protection

Broad-spectrum sunscreen as well as protective clothing are among the best preventative measures against the sun’s harmful rays. After one trip to the drugstore, you’ll understand that there are a lot of sunscreens available. So, which one do you buy? You might be wondering which level of SPF offers the most effective protection. SPF, or Sun Protection Factor, is a measure of how long you can be exposed to the sun before you begin to burn (i.e. SPF 30 means that it would take you 30 times longer to burn than without sunscreen).

  • SPF 15 blocks up to 93% of UVB rays
  • SPF 30 blocks up to 97% of UVB rays
  • SPF 50 blocks up to 98% of UVB rays

Be sure to purchase a sunscreen with broad-spectrum protection which means that it protects against both UVA and UVB radiation from the sun. SPF 30+ combined with protective clothing such as long-sleeved shirts, hats and UV rated sunglasses can help prevent sun damage that could lead to various skin cancers and irreparable eye damage.  


Skin Cancer Foundation resources on UV Radiation

FDA Resources on Ultraviolet Radiation

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