According to the CDC, Utah has the highest melanoma rate in the United States. Utah's age-adjusted rate of 42.3 per 100,000 persons is roughly double the national average and well above second place Vermont (35.7). Most skin cancers result from UV exposure, typically from sunlight, although there are other sources such as tanning beds.
The sun emits ultraviolet radiation in three bands: UVC (315-400 nanometer wavelength), UVB (280-315 nm), and UVA (100-280 nm). The UVC is largely absorbed by the atmosphere before reaching the surface. Some, but not all of the UVB is also absorbed, whereas a good chunk of the UVA makes it through. Thus, the UV reaching the Earth's surface is comprised primarily of UVA, with some UVB.
How much depends on many factors. One is the sun angle. When the sun is high in the sky, its rays pass through less atmosphere. In contrast, when it is lower in the sky, it passes through more atmosphere. This is illustrated, somewhat simplistically below since I'm not accounting for curvature and several other minor effects related to the distribution of ozone in the atmosphere.
All else being equal, this effect results in UV levels being highest when the sun is highest in the sky. In the mid-latitudes, UV levels are higher in the summer than the winter highest at solar noon (which in Utah in summer is actually fairly late in the day — 1:25 PM today).
Cloud cover, water vapor concentrations, and pollution also affect the amount of UV radiation reaching the ground. In addition, the height of the tropopause and the depth of the stratosphere, which contains large concentrations of ozone molecules that absorb UV varies. When we are under the influence of an upper-level ridge, the tropopause is high and the total stratospheric ozone if often lower.
Altitude also plays some role. There's simply less atmosphere above you as your elevation increases. According to the World Health Organization, UV radiation increases by 10% to 12% for every 1000 m increase in elevation. The exact number would depend on the time of year, time of day, latitude, and weather, but that equates to about a 20-25% increase from the Salt Lake City International Airport to the higher Wasatch peaks at 11,000 ft.
Finally, reflection from the surface can also be important, with snow reflecting up to 80% of the UV radiation.
Recently, Powder Magazine reported that in a recent study by the Huntsman Cancer Institute and University of Utah Health, 38 of 394 employees who were voluntarily screened at two Utah ski resorts were diagnosed with skin cancer.
Utah is a tough place for skin cancer for a number of reasons. It's elevated. There isn't much natural shade (e.g., tree cover). Much of the population is of European descent. The weather is outstanding and invites outdoor activity, especially in the summer when the sun and potential for UV exposure is highest.
I often tell people that I am "solarly challenged" and that people of Irish decent (i.e., me) shouldn't live outdoor adventure lifestyles, especially in Utah.
I've become much more aggressive about sun protection in the past couple of years. I hike and bike as much as possible in the morning and evening. I wear clothes as much as possible. I wear hats as much as possible. I carry a tube of sunblock in my pocket and apply much more frequently than in the past. I try and suffer through the heat and stay covered as much as possible.
I am constantly on the hunt for cool coverings for my body. One of the best purchases I made was the Outdoor research Chroma Full Sun gloves, which are super thin but UPF50.
I wear these now whenever hiking or ski touring in the spring. Of all the sun gear I've bought, they are the only purchase I would rate at five stars. I'm waiting for a sale and then I'll buy a couple pairs more. The only way to improve them would be to add a patch to allow for smart phone interaction.
If you have clothing recommendations, please pass them along.