"Most everyone is aware of the risks associated with UVB exposure, however there are real risks associated with UVA exposure including skin aging, DNA destruction and even skin cancer. Protecting your skin from UVA rays is just as important as protecting yourself against UVB rays."
Dr. Henry Lim, Vice President-Elect, American Academy of Dermatology and Chairman of Dermatology, Henry Ford Hospital, Detroit, MI
Did you know...
Experts say up to 80% of skin aging is due to UVA rays.1
Over 30 years, the left side of this teacher’s face aged faster due to UVA
exposure through a window in her classroom. Just compare the two sides!
Photos: Professor J. Leyden.
Photos not retouched.
UVA rays have been linked to skin cancer
There is significant scientific evidence that UVA rays contribute to skin cancer by suppressing the immune system.2


Photos:
Dr. J. Leyden
Up to 95% of UV rays that reach the skin are UVA rays
UVA radiation levels have small fluctuations during the day and are present year-round, even in the winter and on cloudy days. UVA rays can even pass through windows and glass, making the indoors, near windows, equally dangerous for your skin.
What is UV?
UV means ultraviolet, and refers to the radioactive rays emitted by the sun. Two types of damaging UV rays reach the earth: UVA and UVB. UVA rays mainly cause Aging, while UVB rays mainly cause Burning. However, SPF (Sun Protection Factor) measures only UVB—not UVA protection.

Experts say up to 80% of skin aging can be attributed to UVA rays.
What are the major differences between UVA and UVB rays?*
Unlike UVB rays, UVA radiation levels have small fluctuations during the day, and are present from sunrise to sunset every day, all year round, even in the winter and on cloudy days, and over time can lead to skin cancer.
UVA rays persist all year round, even in the winter– unlike UVB rays.
UVA rays exist from sunrise to sunset, even on cloudy days – unlike UVB rays.
UVA rays pass through windows and glass - unlike UVB rays.
UVA rays penetrate deeper into the dermis than UVB rays
While UVB rays remain primarily at the epidermal level and are partially blocked by the strateum corneum, UVA rays penetrate deeper into the dermis or base layer of the skin.
  • UVA activates the melanin stored in the epidermis, and produces a pigmentation effect visible within one hour but usually fades in 24 hours.
  • UVA penetrates the epidermis where connective tissue and blood vessels exist. The result is a loss of elasticity that causes the skin to sag, wrinkle, and age prematurely.
  • UVB penetration primarily remains at the epidermis level.
  • A large dose of UVB radiation will cause acute sunburn, redness, burning sensation, and blistering.
  • UVB rays stimulate the formulation of melanin, causing a significant pigmentation of the skin. This darkening effect will be evident after approximately 24 hours and is relatively long-lasting.
1 Documentation on file at La Roche-Posay.
2 Clinical study: Dr. A. Kligman. 2000 AAD interview entitled “Is Daily Photo-protection a Rational Ideal?”
* Illustrations not to scale.