From the Research
A broad spectrum sunscreen provides protection against both UVA and UVB rays, but the specific UVA rating isn't indicated by the term "broad spectrum" alone, and according to the most recent study 1, it must pass the FDA's critical wavelength test, meaning they protect against UVA rays with wavelengths of at least 370 nm. When considering the UVA rating of a broad spectrum sunscreen, it's essential to look beyond the label and understand the ingredients and their effectiveness in protecting against UVA radiation.
- The FDA's critical wavelength test is a crucial factor in determining the UVA protection of a sunscreen, as it measures the sunscreen's ability to protect against UVA rays with wavelengths of at least 370 nm 1.
- Ingredients like avobenzone, zinc oxide, or titanium dioxide are effective UVA filters, and their presence in a broad spectrum sunscreen can provide comprehensive protection against both UVA and UVB rays 2.
- Proper application is also crucial, with about one ounce (a shot glass full) of sunscreen needed for full-body coverage, and reapplication every two hours or after swimming or sweating is necessary to maintain protection 1.
- The SPF number on the bottle primarily indicates UVB protection, not UVA, so it's essential to choose a broad spectrum sunscreen with SPF 30 or higher for optimal protection 3.
- The mechanism of action of metal oxide sunscreens, such as titanium dioxide and zinc oxide, is primarily through absorption, not reflection or scattering, providing UV protection via semiconductor band gap mediated absorbance of UV photons 4.