The science of sunshine and UV radiation

ST. JOSEPH, Mo. (News-Press NOW) -- Lots of sunshine is expected over the weekend and into the start of next week. Everyone loves when the blue sky is out, but many forget to protect their skin from potentially harmful UV radiation. 

While the sun’s rays are essential to life on earth, ultraviolet radiation, a particular wavelength of  “sunlight” beyond the visible spectrum, can be damaging to humans. Some UV radiation is filtered by the ozone layer of Earth’s atmosphere, including most UV-B and UV-C rays. Conversely, UV-A radiation penetrates the ozone layer and poses a risk to humans, especially those with excessive sun exposure.

Time of year and weather conditions influence how much UV radiation reaches Earth’s surface. Not surprisingly, UV levels peak on the summer solstice in late June, when the sun’s energy is pointed most directly on the northern hemisphere. 

Clouds also affect UV levels, although most offer limited protection. A thick blanket of clouds can block as much as 69% of UV radiation, while partial cloud cover may only block 10% to 30% . In some cases, certain types of clouds can even enhance UV radiation, this includes thin cirrus clouds which can scatter and reflect light back down to the surface. 

Ultraviolet radiation is quantified daily using the “UV Index”, which takes into account calendar date, location, and weather conditions. At a UV index of 6, the risk of getting sunburned significantly increases. A UV index of 6–7 is considered high, 8–10 is very high, and 11 or above is extreme. During May, UV levels can range between 6 and 10 locally, which means you shouldn’t wait until the heart of summer to start following sun safety tips.

If you know you’ll be outside for an extended period—whether golfing, gardening, or enjoying the park—it’s important to apply sunscreen with an SPF of 15 or higher, depending on your skin’s needs. Make sure to reapply sunscreen multiple times throughout the day, especially during prolonged sun exposure. Hats, sleeves, and shade are also helpful, especially if sunscreen isn’t an option. With proper precautions, the benefits of a bright sunny day can be best enjoyed.