UVA vs. UVB: What Each Ray Does to Your Skin and Why It Matters
Once you know what UVA and UVB each do, you will understand why broad spectrum is the one word that actually matters in the sunscreen aisle.
UVA (320 to 400 nm) penetrates deeper into the skin and drives aging and contributes to skin cancer, while shorter-wavelength UVB (290 to 320 nm) reaches the epidermis and is the main cause of sunburn; UVC (under 290 nm) is completely absorbed by the ozone layer, per the FDA.
The FDA explains that UVA and UVB both contribute to skin cancer and premature aging, which is why it recommends broad-spectrum products that are tested against both bands rather than UVB alone.
Questions we get a lot
What is the difference between UVA and UVB rays?
UVA rays have a longer wavelength (320 to 400 nm) and penetrate deeper into the skin's dermis, driving aging and contributing to skin cancer. UVB rays are shorter (290 to 320 nm), reach the epidermis, and are the main cause of sunburn. Both contribute to long-term skin damage, which is why broad-spectrum protection matters.
What does broad spectrum mean on a sunscreen label?
Broad spectrum means the product has been tested to protect against both UVA and UVB radiation, not just the UVB that causes sunburn. Because UVA penetrates deeper and drives aging, a sunscreen that only blocked UVB would leave you exposed to significant damage. Choosing broad spectrum ensures coverage across both bands.
Do I need to worry about UVC rays?
Not from sunlight. UVC has the shortest wavelength (under 290 nm) and is the most energetic, but it is completely absorbed by the ozone layer before it reaches the ground. The rays you actually need to protect against day to day are UVA and UVB, which is what broad-spectrum sunscreen addresses.
r/SkincareAddiction: 'I get that SPF blocks burning, but what is broad spectrum actually doing differently? Is it worth paying more for?'