What is UV Index and How Does it Affect Your Skincare Routine?

You’ve probably heard the term “UV” tossed around when people talk about sunscreen, but do you know how the index scale actually works, or how it can impact your skin? Ignorance is certainly not bliss on this occasion because failure to mind the daily UV index could lead to sun damage that accelerates the signs of aging or, worse yet, leads to the development of dangerous skin cancer.

We’re here to explain the UV index in simple terms you can understand. Apply what you learn to adjust your skincare routine and maintain a radiant complexion that defies the test of time.

History of the UV Index

The UV index was invented by three Canadian scientists in 1992. Their goal was to create a tool that could help protect Canadians from overexposure to the sun’s ultraviolet (UV) radiation—and they accomplished it. Although the initial UV index was on a scale of 1-10, and the values were based on those usually found in the region, it wasn’t long before the World Health Organization (WHO) recognized the tool’s importance.

WHO adopted the UV index as part of its international program and made the scale open-ended to include more southerly countries. Now, UV index values as high as 14 can be found in tropical parts of the world. But what do these numbers actually measure?

UV index numbers

UV Index Score Values

Essentially, the UV index measures the strength of the sun’s UV rays; the greater intensity, the more damage UV rays can do to your health. The index values are grouped into 5 levels of risk:

  • Low (0-2)
  • Moderate (0-5)
  • High (6-7)
  • Very High (8-10)
  • Extreme (11+)

The higher the number on the scale, the stronger the sun’s rays are forecasted to be—and the more sun protection you’ll need to defend against exposure to harmful UV light.

UV Index Forecast Calculations

So, what happens if you’re packing for a vacation and notice there’s a high UV index forecasted on the weekend you’re set to arrive? Do you stock up hats and sunscreen, or is there a chance that the index could drop to a lower intensity? Sort of, but not really.

The forecast on the UV index is much more accurate than other types of weather patterns, such as an “80% chance of rain” that never arrives, or a Level 2 hurricane that reaches a Level 3 status by the time it hits the shore.

On the contrary, the UV index score is based on three things:

  • The thickness of the ozone layer in the atmosphere
  • The height and angle of the sun above the horizon
  • The amount of cloud coverage in the location

Thick clouds can reduce the amount of UV light that penetrates the earth, so if an unexpected storm were to roll in, the index score would drop. But the ozone thickness fluctuates on a daily basis, as does the sun’s position in the sky depending on earth’s orbit.

UV index and ozone layer

When the sun is high overhead, its light rays cast directly down to the ground, taking the shortest possible route through the atmosphere. This is when the UV is strongest. The ozone layer absorbs UV light, so when the sun is lower to the ground, less UV reaches the surface.

UV Index & Skincare Implications

How does all this science play into your skincare routine at home? Well, even just 15 minutes of unprotected exposure to UV radiation can damage skin and increase your risk of skin cancer. Sometimes, we can see and feel sun damage shortly after it occurs:

  • Changes in color tone (such as tan, pink, or red)
  • Skin that’s hot to the touch
  • Pain, swelling, and tenderness
  • Blisters filled with fluid that can pop

In the case of severe sunburns, when the UV index is very high, you might also experience headache, fever, nausea, and fatigue. But even on the days when risk is low, or your skin doesn’t show visible signs of sun exposure, it doesn’t mean that underlying damage hasn’t occurred to your DNA.

UV radiation penetrates the outer skin barrier and passes into deeper layers where they can damage the structural collagen that supports the walls of the tiny blood vessels in the skin tissue. The UV light particles (known as photons) promote the formation of free radicals, which are highly reactive molecules that attack cellular formation and functioning.

UV radiation impact on skin

A gradual accumulation of free radical damage occurs over time and presents itself with signs of premature aging such as:

  • Wrinkles
  • Fine lines
  • Dark spots
  • Hyperpigmentation

Skin texture tends to become leathery and brittle because it lacks the elastic, stretchy quality it once had in its youth. You can reverse some sun damage, but you can’t erase it entirely. That’s why it’s important to take your skincare very seriously at every stage in life and the sooner, the better—so start now by adjusting your daily routine around the forecasted UV index along with practicing proper sun safety.

How to Tend to Your Skin When the UV Index Is High

Sunscreen should always be a part of your morning skincare regimen, but be sure to amp up your application with a broad-spectrum sunscreen to defend against both UVA and UVB rays when the index presents an increased risk.

Mineral sunscreen is often recommended by dermatologists for those with sensitive skin as it is less likely to cause a reaction compared to chemical counterparts. Whichever type of formula you use — brush-on powder, lotion, aerosol spray — the FDA recommends reapplying every two hours to maintain all-day protection.