How to choose a sunscreen? Choose a broad-spectrum sunscreen with an SPF or “sun protection factor” 15 or more. Remember to choose a product resistant to water if you intend to go in the water. What does the abbreviation UVB? The abbreviation UVB is ultraviolet B. These rays are the primary cause of sunburn, skin aging and skin cancer. UVB rays are most intense between 11 am and 16 pm during the summer. UVB rays are more powerful and more dangerous to the skin than UVA. Their effect is felt mainly on the surface of our skin. What does the abbreviation UVA?