What is the difference between UVA and UVB rays?

There are many different types of rays present in sunlight. The rays that are most damaging to our skin are called ultraviolet (UV) rays. There are two basic types of ultraviolet rays that reach the earth’s surface—UVB and UVA. UVB rays are responsible for producing sunburn. The UVB rays also play the greatest role in causing skin cancers, including the deadly black mole form of skin cancer (malignant melanoma).

UVA rays also play a role in skin cancer formation. In addition, the UVA rays penetrate more deeply into the skin and play a greater role in premature skin aging changes including wrinkle formation (photoaging). There are approximately 500 times more UVA rays in sunlight than UVB rays. Therefore, in addition to protecting your skin from the effects of UVB rays, it is also very important to protect from the damaging effects of the more numerous UVA rays. Traditional chemical sunscreen products have been more successful at blocking UVB rays than UVA rays.

UV ray index

A number between 0-15 is given to cities and areas around the United States to rate the strength of ultraviolet rays. Find your area’s ultraviolet ray rating through the National Weather Service and determine your risk factors and take the necessary precautions.

Rating Risk Minutes to burn Precautions
0 - 2 Minimal 60 minutes Sunscreen, UV sunglasses
2 - 4 Low 45 minutes Sunscreen, UV sunglasses
4 - 6 Moderate 30 minutes Sunscreen, UV sunglasses and hat
6 - 10 High 15 minutes Sunscreen, UV sunglasses, hat and umbrella
10 - 15 Very High 10 minutes Sunscreen, UV sunglasses, hat, umbrella and avoiding midday sun
Last reviewed: 
April 2018

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