It’s safe to say that we Californians get more than our fair share of sun! However, overexposure to the sun’s ultraviolet rays—especially unprotected exposure—can cause our skin to breakdown, damage our eyes, and even cause skin cancer. There are other contributing factors to getting skin cancer, such as genetics and environment, but the more sunburns we get, the more we increase our chances of getting it and causing inflammation in our skin. This also leads to premature aging (photo-aging) in the form of discoloration, early onset wrinkles, and the degradation of precious collagen.
If you’ve been following along on this series, we started by talking about correct sunscreen application and what you can do to help mitigate the rays of the sun. We’re now moving on to discuss some fundamental concepts, like the differences between UVA and UVB rays and what SPF and broad-spectrum sunscreen claims mean.
First things first, what is the difference between UVA and UVB rays?
UVA rays, also known as long ultraviolet rays or “aging” rays, enter the dermis (deeper layer of the skin) and are the main culprits behind premature aging, which can manifest as wrinkling and or discoloration. They generate reactive oxygen species (ROS) that can damage DNA within cells via indirect photosensitizing reactions.[1]
UVA rays account for approximately 95% of the ultra violet light that we’re exposed to on any given day. They are present all day, every day, rain or shine and at the same intensity. UVA rays can even penetrate through glass (think, your skylight or dashboard).
The wavelength of UVA light is 320 nm to 400 nm. There are two types of UVA rays (UVA1 & UVA2), ranging from 340–400 nm and 320–340 nm.
UVB rays or “burning” rays are absorbed by the epidermis and induce an inflammatory response, which in turn, causes sunburn. These rays are directly absorbed by DNA, which causes molecular rearrangements or mutations.[2] Unlike UVA rays, UVB rays are more prevalent in sunny climates and the intensity of these can vary greatly depending on time of day, geography, and season. And unlike UVA rays, UVB rays can be blocked by windows.
The wavelength of UVB light is 290 nm to 320m nm, a shorter length than UVA light.
Many sunscreen formulations account for these differences in wavelength, and do so by incorporating specific filters or a combination of filters to help protect from both forms of UV light.
What does SPF mean and what does the number alongside it signify?
Contrary to popular belief, wearing sunscreen does not completely prevent your skin from burning or block you from harmful rays. It acts as a “screen,” reducing the number of photons from UV light that penetrate your skin. The higher the SPF or sun protection factor, the less UV passes through, however protection does not increase exponentially, the greater the SPF. For example, an SPF 30 filters approximately 96.7% of UV, compared to 98% of an SPF 50.
As we covered in our first article of this series, dermatologists and the AAD suggest re-applying sunscreen every two hours to maintain sunscreen efficacy, irrespective of the sun protection factor. As humans, we are naturally active, and as we go about our day, the product will wear off or break down due to perspiration and environmental factors.
And what does broad spectrum mean?
When a sunscreen has a broad spectrum claim, it signifies that the product has an ability to protect against both UVA and UVB radiation. The method conducted to verify this is an in vitro test that measures a sunscreen’s transmittance/absorbance of ultraviolet (UV) radiation across both UVA and UVB regions of the spectrum.[3]
If the product is not labeled broad spectrum, SPF alone does not tell consumers anything about the UVA protection the product offers. According to FDA regulations, if the product is labeled broad spectrum, it means that the UVA protection is proportional to the UVB protection.
Remember, UVA rays cause most of the aging effects we see in our skin, so it’s wise to opt for broad spectrum sunscreen, with a minimum SPF of 30, for areas you want to help maintain a more youthful appearance.
Stay tuned for the last article in this series where we talk about mineral and chemical sunscreens, and how to figure out which sunscreen is right for you!
Written by Maya
Reviewed by Drs. Fardin and Smith
[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3709783/
[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3709783/
[3] https://www.fda.gov/regulatory-information/search-fda-guidance-documents/labeling-and-effectiveness-testing-sunscreen-drug-products-over-counter-human-use-small-entity