How UVA and UVB Differ
How UVA and UVB Differ — two bands of ultraviolet light that reach the skin in different ways, with UVA penetrating deeper and driving aging while UVB acts more on the surface and causes burning. Both contribute to skin cancer, which is why broad-spectrum protection covers the full range.
Key points
- UVA has a longer wavelength, penetrates into the dermis, and is the main contributor to photoaging and wrinkles.
- UVB has a shorter wavelength, affects the outer layers, and is chiefly responsible for sunburn.
- UVA levels stay relatively constant through the day and year, while UVB peaks midday and in summer.
- Broad-spectrum sunscreens are formulated to shield against both bands, since SPF alone measures mainly UVB protection.
Frequently asked
A helpful way to remember the difference between UVA and UVB?
Many people use the mnemonic that UVA is for aging and UVB is for burning, though both types damage DNA and increase skin cancer risk.
Does a high SPF protect against UVA?
SPF primarily reflects UVB protection, so you need a product labeled broad-spectrum to ensure meaningful defense against UVA as well.
Related topics
This is a foundational entry in the SYNC Skin Encyclopedia and is expanded over time. Educational information only — not medical advice.
