UVA vs UVB: What's the Difference and Why It Matters

When people talk about sun damage, they usually think about sunburn. But sunburn is just one part of the story. The UV spectrum contains two types of rays that affect your skin differently, cause different types of damage, and require different protection strategies.

Here is what you actually need to know about UVA and UVB, and why both matter for your long-term skin health.

UVB Rays: The Burning Rays

UVB rays have shorter wavelengths and higher energy than UVA rays. They affect the outer layers of your skin and are the primary cause of sunburn. They are also the rays that the SPF number on your sunscreen is measuring protection against.

SPF 30 blocks approximately 97% of UVB rays. SPF 50 blocks approximately 98%. The difference between SPF 30 and SPF 50 is smaller than most people assume, which is why reapplication matters more than chasing higher SPF numbers.

UVB rays also play the primary role in the development of skin cancer. They cause direct DNA damage in skin cells that can lead to mutations over time.

UVA Rays: The Aging Rays

UVA rays have longer wavelengths that penetrate deeper into the skin, reaching the dermis where collagen and elastin live. UVA exposure is the primary driver of photoaging -- the wrinkles, loss of elasticity, and dark spots that accumulate with years of sun exposure.

Here is what makes UVA more insidious than UVB: UVA rays are present at relatively constant intensity throughout the day and across all seasons. They penetrate cloud cover and glass. You are being exposed to UVA rays on overcast days, through car windows, and year-round -- not just during peak summer hours.

UVA rays also contribute to skin cancer development, though through a different mechanism than UVB. Both matter.

What Broad Spectrum Actually Means

A sunscreen labeled broad spectrum has been tested to protect against both UVA and UVB rays. This is not optional. A sunscreen that only protects against UVB will prevent sunburn while leaving you completely exposed to the aging and cancer risk of UVA radiation.

All SolRX formulas are broad spectrum, protecting against both UV wavelengths. This is the baseline for any sunscreen worth using.

The SPF Number Only Measures UVB

This surprises most people. The SPF rating on your sunscreen only reflects protection against UVB rays. There is no equivalent standardized rating system for UVA protection in the United States.

The broad spectrum designation tells you UVA protection is present, but not how much. This is one reason mineral sunscreens with zinc oxide are considered particularly valuable: zinc oxide provides robust protection across both UVA and UVB wavelengths on its own, without needing multiple chemical filters to achieve the same coverage.

UV Exposure Is Year-Round

UVB rays are strongest in summer and peak between 10 AM and 4 PM. UVA rays are constant. This is why dermatologists recommend daily sunscreen application regardless of season or weather.

Daily SPF protects against the cumulative UVA damage that drives premature aging and long-term cancer risk, not just the acute UVB exposure that causes a visible burn.

Practical Takeaways

• Choose broad spectrum sunscreen. This is non-negotiable for real protection.

• SPF 30 is sufficient for most daily use. Go higher if you are spending extended time outdoors.

• Reapply every 2 hours in direct sun. SPF does not last all day.

• Apply daily, even in winter and on cloudy days. UVA exposure is constant.

• Zinc oxide provides the broadest spectrum mineral protection available.