What the UV index tells us, but does not further reveal

If you’ve ever watched a weather forecast, you’ve probably come across the term ‘UV index’, a number that tells us how strong the sun’s rays will be that day. But do you really understand what this index means and what it doesn’t tell us about the solar radiation that can affect our skin? This is especially important for teenagers, outdoor athletes, and outdoor professions that spend a lot of time outdoors. This blog explains the UV index, what it means but also what it doesn’t say.

What is a UV-index

The UV index is an internationally standardized measure that indicates the intensity of ultraviolet (UV) radiation on earth. The measurement is carried out using special devices, called spectrometers, which measure the amount of UV radiation in different wavelength ranges.

The UV index measures the intensity of UVB and to a lesser extent UVA radiation from the sun.

The UV index is calculated based on various factors that influence the strength of solar radiation. It is important to understand these factors to know how and why the UV index changes and what this means for our protection against the sun.

1. Sun Altitude: This is the main factor. The higher the sun is in the sky, the more intense the UV radiation. Therefore, UV radiation is stronger around midday and during the summer months, when the sun is at its highest point in the sky.
2. Ozone Layer: The ozone layer in the atmosphere plays a crucial role in absorbing part of the UV radiation. Variations in the thickness and condition of the ozone layer can cause daily and seasonal differences in UV intensity. Thinner ozone means more UV radiation reaching the earth’s surface.
3. Cloudiness: The presence of clouds can reduce the amount of UV radiation reaching the Earth, but not completely block it. Interestingly, thin or white clouds can sometimes enhance UV radiation by reflecting and dispersing it.
4. Altitude above sea level: At higher altitudes, the atmosphere is thinner and less capable of filtering UV radiation. This means that people in higher areas are exposed to stronger UV radiation.
5. Reflective surfaces: Surfaces such as snow, sand, water, and even grass can reflect UV rays and increase their intensity. For example, snow can reflect almost 90% of UV radiation, which significantly increases exposure.

The measurements are then combined into a mathematical formula that takes into account the different wavelengths of UV radiation and their effects on human skin. The resulting value, which lies between 0 and 10, is called the UV index.

Interpretation of the current UV index:

0-2: Low
Minimal protection is needed. It’s safe to be outside, but it’s always good to apply sunscreen on exposed skin, especially if you are sensitive to sunburn.

3-5: Average
Protection with sunscreen and covering clothing is recommended. Put on sunglasses to protect your eyes and try to avoid direct sunlight around midday, when the sun is strongest.

6-7: High
Extra protection is required. Apply plenty of sunscreen with a high SPF and wear protective clothing, such as long pants, a long-sleeved shirt, and a wide hat. It’s also wise to limit sun exposure between 10 a.m. and 4 p.m., when UV radiation is at its highest.

8-10: Very High
Avoid exposure to the sun and seek shade, especially during midday hours. Wear sunscreen with a very high SPF, protective clothing, a wide hat, and UV-protective sunglasses. It is best to stay indoors when the sun is at its strongest.

11+: Extreme
Maximum protection required. Stay indoors as much as possible and avoid all direct sun exposure. If you must go outside, ensure full coverage of the skin with UV-protective clothing, a wide hat, sunglasses and sunscreen with the highest possible SPF. Regularly check the skin for signs of sunburn such as pressure relievable redness and blisters.

In the past 26 years, the Netherlands has rarely experienced a UV index higher than 8. In contrast, in Suriname a UV index of up to a value of 13 occurs.

UV index does not indicate UVA intensity and HEV light

UV rays that reach our earth consist of UVA and UVB rays. UVB radiation is the main cause of sunburn and plays a crucial role in the development of skin cancer. UVA radiation, on the other hand, penetrates deeper into the skin than UVB radiation and is responsible for premature skin aging, such as wrinkles and pigmentation spots.

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Even on days with a low UV index, it is worthwhile to consider protection against UVA rays. The UV index mainly reflects the intensity of UVB radiation, but UVA rays are almost constantly present during all daylight hours, throughout the year, regardless of the UV index.

This means that UVA radiation can still pose a significant risk, even on days when the UV index is low.

Commonly Heard Misconceptions:

In the Netherlands

In the Netherlands, just like in many other Northern European countries, the intensity of UVA rays remains fairly consistent throughout the year, regardless of cloud cover, rain, or snow. UVB rays are stronger in the spring and summer period. This is why people tend to burn more easily in these seasons. During autumn and winter, UVB rays are less intense, but this doesn’t mean there’s no risk of skin damage.

You Don’t Notice UVA Rays

Although UVA rays do not cause the immediate, burning sensation of sunburn like UVB rays, they are nevertheless harmful. They penetrate deeply into the skin and generate free radicals, which can cause unnoticed damage to the dermis, where elastic and collagen fibers and fibroblasts are located. UVA rays are responsible for premature skin aging, such as wrinkles and skin sagging, and also increase the risk of skin cancer.

Risks of UVA Radiation and Air Pollution

An additional risk of UVA radiation is the interaction with air pollution. Research shows that UVA rays can react with certain pollutants in the air, which also leads to the formation of free radicals. Free radicals are unstable molecules that lack electrons, making them highly reactive with other molecules. These free radicals cause oxidative and genetic damage to the skin cells, leading to photo damage such as pigmentation spots and wrinkles, and skin cancer.

Why UVA protection is important:

• Skin aging and wrinkles: UVA rays penetrate deeper into the skin than UVB rays and are primarily responsible for premature skin aging, including wrinkles and skin sagging.
• Skin Cancer: Although UVB is more often associated with skin cancer, UVA also contributes to skin cancer risks by penetrating deeper into the skin and causing damage.
• Consistent exposure: UVA radiation is consistent throughout the year, regardless of the season or latitude, and can even penetrate through clouds and glass.

Visible HEV Light and the Skin

In addition to the well-known UV radiation from the sun, there is another form of light that can affect our skin: HEV light. HEV light, often called blue light, not only comes from the sun, but also to a lesser extent, is emitted by digital screens such as smartphones, tablets, and computers. The UV index says absolutely nothing about visible HEV light.

One of the main ways in which HEV light can damage the skin is by the production of free radicals.

Specific challenges for Fitzpatrick skin type 3 and higher

In individuals with Fitzpatrick skin type 3 and higher, who have a darker skin tone, a specific protein called opsin-3 plays a role in how their skin responds to blue light. Opsin-3, present in melanocytes (the pigment cells in the skin), is sensitive to blue light and can influence the production of pigment. Exposure to HEV light can cause opsin-3 to respond by activating the melanocytes to produce more melanin, which can lead to the emergence of pigment spots. This happens unnoticed and can result in uneven pigmentation, especially if the skin is unprotected.

Harmful effects of HEV light on the skin

• Early skin aging: HEV light can stimulate the production of free radicals, which break down cellular structures such as collagen and elastine. This leads to wrinkles, loss of firmness, and a dull skin tone.
• Pigmentation spots: In people with a dark skin color (skin type 3 or higher), HEV light can increase the production of melanin, which can lead to pigmentation spots and an uneven complexion.
• Cellular damage: Long-term exposure to HEV light can cause cellular damage, potentially increasing the risk of skin cancer.

Misconceptions in practice about UV index summarized

There are some common misconceptions about the UV index that can lead to inadequate protection against the harmful effects of sunlight. Here are the main misconceptions:

1. The UV index measures all UV rays: Many people think that the UV index is a measure of all types of UV radiation, including UVA and UVB. However, the UV index primarily measures the intensity of UVB radiation, which is responsible for sunburn and has a direct impact on the risk of skin cancer. The index does not specifically indicate the intensity of UVA rays, which are more responsible for skin aging and also contribute to the risk of skin cancer.
2. A low UV index doesn’t mean sun protection isn’t necessary: Some people believe that a low UV index (for example, under 3) means that sunscreen isn’t necessary. However, this is not correct, as UVA rays, which aren’t well measured by the UV index, are consistent throughout the day and can also be harmful. It’s important to wear sunscreen daily, even with a low UV index.
3. The UV index is only important in the summer: There is a general assumption that the UV index is only relevant during the summer months when the sun is at its strongest. Although the UV index is often higher in the summer, UVB rays and especially UVA rays can also be harmful in the fall, winter, and spring, particularly in areas with snow that can reflect UV rays and increase exposure.
4. The UV index is only important on sunny days: Many people ignore the UV index on cloudy days, but up to 80% of UV rays can penetrate clouds. This means that the skin is still exposed to UV rays, even if the sun is not visible.
5. The UV Index does not cover blue light or HEV rays: Although the UV Index provides an indicator of the risks from sunlight, it doesn’t measure exposure to High-Energy Visible (HEV) light or blue light, which can also contribute to skin aging and potentially other health problems. Protection against HEV light is often overlooked.
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What does this mean for you?

Considering the risks of both UVA and UVB radiation, it is essential to apply adequate sun protection throughout the year, regardless of the weather or season. Here is a clear and easy to remember advice on sun protection for you in the Netherlands:

UVA radiation: Always present

• Forever Present A: UVA rays are always present, regardless of the season or weather.
• A for Aging: UVA rays are a major cause of premature skin aging.
• A for Asymptomatic: You don’t directly feel or notice the UVA rays.

UVB Radiation: More Important in Spring and Summer

• B for Burn: UVB rays are stronger in the spring and summer and are responsible for sunburn. Advice: Use a sunscreen with at least SPF 30 in the spring and summer to protect your skin from burning and the increased risk of skin cancer.

Protection against visible light

• Especially important for people with tinted skin, sun allergy or pigment spots such as melasma. Advice: Consider products that also offer protection against high-energy visible light (HEV-light), often referred to as blue light, which can contribute to skin aging and pigmentation problems.

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