UVA vs. UVB: What Your Skin Is Actually Dealing With
Most of us know the sun emits UV light and that sunscreen matters. But understanding exactly how UV light works, and why it affects skin differently depending on conditions, changes how you approach every day outdoors.
Two Types of UV. Two Very Different Stories.
The two primary types of UV radiation that reach the Earth's surface are UVA and UVB. Both affect the skin, but in very different ways.
UVA: The Aging Ray
UVA makes up approximately 95% of UV radiation at the surface. It penetrates deeper into the skin, is present all day long, and does not let up on cloudy days. UVA is responsible for:
• Premature aging, wrinkles, and loss of elasticity
• Hyperpigmentation and age spots
• Collagen breakdown and cumulative long-term damage
Here is what surprises most people: UVA intensity stays relatively constant throughout the day and penetrates glass. You are receiving UVA exposure while driving, sitting near a window, or working in a sunny room.
UVB: The Burning Ray
UVB primarily affects the outer skin layers and is the main cause of sunburn. Unlike UVA, its intensity shifts based on time of day, season, and location. UVB is strongest between 10 AM and 4 PM. UVB causes:
• Sunburns and skin reddening
• Direct DNA damage
• Increased skin cancer risk
Tanning vs. Burning: Not the Same Thing
A tan is primarily triggered by UVA exposure. A burn is caused by UVB. They are not different degrees of the same thing. This matters because you can accumulate real skin damage on a cloudy afternoon with no burn, no heat, and no warning.
Clouds reduce visible sunlight but allow a significant amount of UV radiation through, especially UVA. Many people spend more time outside on overcast days because it feels cooler and safer. That assumption leads to more UV exposure, not less.
Your skin responds to UV radiation, not temperature and not brightness. Do not let clouds or a cool breeze convince you otherwise.
Sun Responsibly ☀️
Dr Debbie Rice, Chief Medical Director, EthoSun