What does the UV index number mean?
FAYETTEVILLE, Ark. (KNWA/KFTA) — Summer has officially begun, and the UV index is only getting higher.
The UV index, or Ultraviolet Index, is a measure of the strength of ultraviolet (UV) radiation from the sun at a particular place and time, according to the National Weather Service (NWS).
But what is UV radiation, and why should we avoid it?
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UV radiation: the good, the bad and the ugly
UV radiation from the sun is a type of energy emitted from the sun. UV radiation from the sun comes in three types: UVA, UVB, and UVC.
UVA and UVB are the ones that reach us and can harm our health.
UVB causes sunburns and increases the risk of skin aging and cancer, while UVA also ages the skin and raises cancer risks by penetrating deeper. Both can damage skin DNA, leading to mutations and potential cancer. UV radiation also harms the eyes, causing issues like cataracts.
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While it’s beneficial for mood and vitamin D, too much UV exposure without protection can cause serious health problems. So how do we know how much sun is too much sun?
That’s where the UV index comes in. The first UV index was created by Canadian weather scientists, making Canada the first country to issue UV level predictions.
The UV index is typically measured between numbers zero and 11. Each number has a different meaning:
The UV Index (The National Weather Service)
Low (0-2) | No SPF needed. – There is low danger from the sun’s UV rays for the average person. |
Moderate (3-5 | Some SPF needed. – There is moderate risk of harm from unprotected sun exposure. |
High (6-7) | SPF needed – There is high risk of harm from unprotected sun exposure. |
Very High (8-10) | A lot of SPF needed – There is very high risk of harm from unprotected sun exposure. |
Extreme (11+) | Stay indoors from 10 a.m. to 4 p.m. – There is extreme risk of harm from unprotected sun exposure. |
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SPF has you covered
Sun Protection Factor, or SPF is a measure of how well sunscreen protects against UVB rays, the type of UV radiation that causes sunburn, skin damage and can contribute to skin cancer, according to the Food and Drug Administration (FDA).
The SPF number indicates the level of protection the sunscreen provides:
SPF 15: Blocks about 93% of UVB rays.
SPF 30: Blocks about 97% of UVB rays.
SPF 50: Blocks about 98% of UVB rays.
The higher the SPF number, the greater the protection, but no sunscreen can block 100% of UV rays. It’s essential to apply sunscreen generously and reapply every two hours, especially after swimming or sweating, to maintain effective protection against sun damage.
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UPF-rated clothing can also provide effective sun protection by blocking or absorbing UV rays. Fabrics with tighter weaves, darker colors, and synthetic fibers tend to offer better protection than lighter, loosely woven fabrics.
When in doubt, wear SPF. Here are some suggestions from the NWS to protect yourself at each level:
Low (0-2) | – Wear sunglasses to protect your eyes on bright days. |
Moderate (3-5) | – Cover up, wear a hat and sunglasses, and use sunscreen with SPF 30 or higher when outdoors. |
High (6-7) | – Limit sun exposure from 10 a.m. to 4 p.m. |
Very High (8-10) | – Wear a wide-brimmed hat and sunglasses for extra protection. |
Extreme (11+) | – Unprotected skin can burn quickly, even in minutes. |
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