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Know the UV Index, Know Your Risk

Woman in the sun wearing a floppy hat and sunglasses to protect here skin from harmful UV radiation.

You've likely heard of The UV Index ... maybe on your favorite weather app or on the nightly news ... but do you really understand it?  

What is the UV Index?

It's a valuable tool that helps you understand the risks associated with sun exposure in your area at a given time ... especially concerning the harmful effects of ultraviolet (UV) radiation on our skin. Using this information enables us to take appropriate precautions and protect ourselves while enjoying the great outdoors.

Understanding the UV Index

The UV Index is a standardized measurement used to convey the intensity of ultraviolet radiation from the sun at a specific location and time.

The World Health Organization (WHO) and the World Meteorological Organization (WMO) jointly developed this scale to help individuals comprehend the potential risks associated with UV exposure and take necessary protective measures.

The index typically ranges from 0 to 11+, with higher numbers indicating greater UV intensity and higher risk.

Factors Affecting UV Intensity

Several factors influence the UV Index readings on any given day:

Time of Day:

UV radiation is strongest between 10 a.m. and 4 p.m., so it's best to plan outdoor activities earlier or later in the day to minimize exposure during peak hours.


UV levels tend to be higher in spring and summer due to the sun's angle and increased daylight hours. However, it's essential to remember that UV rays can still be harmful during other seasons, even on cloudy days.

Latitude and Altitude:

UV intensity is higher at higher latitudes and altitudes, meaning mountainous areas or regions closer to the equator often experience stronger UV radiation.

Cloud Cover:

Clouds can block some UV rays, but not all of them. Even on overcast days, a significant amount of UV radiation can still reach the Earth's surface, so sunscreen should be applied regardless of cloud cover.

Ozone Layer:

The ozone layer acts as a natural shield against harmful UVB radiation. Damage to this protective layer, such as the ozone hole, can lead to higher UV levels reaching the Earth's surface.

Understanding the UV Index Levels

Here are the different UV Index levels and the precautions recommended for each:

Low (0-2)

A UV Index of 0 to 2 indicates a low risk of harm from UV exposure. While the risk is minimal, it's still essential to practice sun safety measures, such as wearing sunglasses, a wide-brimmed hat, and applying sunscreen with an SPF of 30 or higher.

Moderate (3-5)

A UV Index of 3 to 5 suggests a moderate risk of harm. During these times, it's crucial to take additional precautions, like seeking shade during peak hours and wearing protective clothing to cover exposed skin.

High (6-7)

A UV Index of 6 to 7 signifies a high risk of harm from UV radiation. Extra precautions are necessary to avoid sunburn and skin damage. Minimize outdoor activities during peak hours and wear sunscreen, protective clothing, and sunglasses consistently.

Very High (8-10)

A UV Index of 8 to 10 poses a very high risk of harm, particularly during midday hours. It's advisable to stay indoors during this period if possible, and if not, take every precaution to protect your skin from the sun's rays.

Extreme (11+)

A UV Index of 11 or higher indicates an extreme risk of harm. During these conditions, it's best to avoid any outdoor activities, especially during peak hours. If you must go outside, wear protective clothing, use a broad-spectrum sunscreen with a high SPF, and seek shade whenever possible.

UV Safety Tips

Regardless of the UV Index level, it's essential to prioritize sun safety whenever you're outdoors:

Apply Sunscreen: Use a broad-spectrum sunscreen with SPF 30 or higher, applying it generously and reapplying every two hours or more frequently if swimming or sweating.

Seek Shade: Stay in the shade during peak hours, typically between 10 a.m. and 4 p.m.

Wear Protective Clothing: Cover exposed skin with lightweight and loose-fitting clothing, a wide-brimmed hat, and sunglasses that block both UVA and UVB rays.

Stay Hydrated: Drink plenty of water, especially on hot and sunny days, to prevent dehydration.

Be Sun Smart: Avoid tanning beds and artificial sources of UV radiation, as they can also cause skin damage and increase skin cancer risk.

Knowledge is Power

Understanding the UV Index and its implications is vital for safeguarding our skin against the harmful effects of UV radiation. By knowing the UV intensity levels, we can take the necessary precautions to enjoy outdoor activities while minimizing the risk of sunburn, premature aging, and skin cancer.

So, before stepping out into the sun, be sure to check the UV Index and follow the recommended sun safety tips to keep your skin healthy and protected all summer long.

Integrated Dermatology of Tidewater Integrated Dermatology of Tidewater Integrated Dermatology of Tidewater, located in Norfolk, Virginia, provides comprehensive personalized dermatologic care to patients of all skin types, conditions, and ages. Medical director Jonathan Schreiber, MD, PhD and the entire professional medical team at Integrated Dermatology of Tidewater approach dermatologic exams from the medical root of an issue, and similarly, cosmetic issues from the science of a treatment, using science-based support and results with the treatment services offered to patients.

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