High elevation, intense sun on snow, and winter inversions.
Most Utahns live at 4,000 feet or higher, with mountain towns much higher, so the air is thinner and the sun stronger. Winter inversions trap polluted air in the valleys, radon is high in parts of the state, and valley fever is present in the southwest.
The Wasatch Front sits around 4,000 to 5,000 feet and ski towns climb well above that. Thinner air means less oxygen per breath. Visitors and newcomers may get headaches and poor sleep at first, and sleeping above about 8,000 feet brings a real risk of altitude sickness.
UV intensity rises about 6 percent for every kilometer of elevation, and snow reflects UV back up at you. On the slopes and trails you can burn in winter as easily as in summer. Over a lifetime that adds to skin cancer and eye damage risk.
In winter, mountains around the Salt Lake Valley trap cold air near the ground, and pollution builds under it. Utah typically has five or six multi-day inversions each winter, and fine-particle levels can reach unhealthy ranges. Fine particles irritate the lungs and are hard on the heart, especially for people with asthma, COPD or heart disease.
Radon is an invisible, odorless radioactive gas that seeps from soil into homes and is the leading cause of lung cancer in people who don't smoke. EPA's map puts several central and eastern Utah counties in Zone 1, its highest-risk category, and the rest of the state in Zone 2.
Valley fever is a lung infection from breathing spores of a soil fungus. A 2006–2015 study of Utah cases found Washington County, around St. George, had by far the state's highest rate, with new construction linked to more cases. Dust from digging and wind stirs up the spores.
Go down to lower elevation and get care for altitude symptoms that worsen with rest. See a doctor for a cough or fever lasting more than a week or two, especially after dust exposure in southern Utah, and mention valley fever. Have any new or changing mole checked.