Many of those who work outside this time of year are subject to some of the moodier days of Mother Nature.
Farmers, construction workers, postal employees, commercial delivery drivers and police officers all spend significant time outdoors. They face a variety of weather conditions: rain, sleet, snow, and the occasional bitterly cold, blue-sky day. Keeping your core body temperature normal and the rest of your body safe takes some preparation. 
Somewhat counter-intuitively, solar radiation can be a hazard in the winter. The sunshine is less intense because of the tilt of the earth; however, clear, cold air doesn’t filter UV radiation as well, especially at high altitude.
If you happen to be in the snow, think of it as a big solar mirror, toasting you from the ground up. There even is a name for a sunburned retina: snow blindness. Sun damage to the skin and eyes is less expected in the winter, but sunglasses and sunblock remain necessary.
Clear, cold air also holds very little moisture. That means your moisture (which is what we are mostly made of) is trying hard to escape. Exercising in the cold can cause losses of two quarts of air an hour from your breath alone. It’s harder to remember hydration when your water bottle is frozen, but it’s vitally important.
The big concern with working in winter temperatures is staying warm. Hypothermia can give you all the coordination of an intoxicated adolescent and injury is all but a certainty.
Hypothermia is the result of the core body temperature dropping below 95 degrees. Symptoms initially result from the body trying to warm itself. Shivering starts mildly, but may get so violent that coordinated movement is impossible. Shivering can more than double heat production.
As the hypothermia progresses, the blood supply in the extremities is partially shut down to conserve heat, which makes the limbs feel thick and difficult to move. The brain stops working well, and confusion can become so profound with severe hypothermia that people often start discarding their clothes and try to burrow.
Maintaining your core body temperature is all about layers. You basically want to turn yourself into a human thermos bottle; layer/air/gap/layer. The first layer is all about wicking, helping sweat to be drawn away to keep the skin dry. Polypropylene synthetics do this very well. They are comfortable, stretchy, and always feel dry.
The middle layer should be a good insulator that traps air. Light-weight, thick clothing such as polar fleece, a wool sweater or synthetic down are ideal for trapping air. You can have several middle layers, each trapping more air.
The top layer keeps the warm air inside, and ideally allows water vapor to escape. This layer also needs to be water, wind and abrasion proof – a tall order indeed. A whole technology of various membranes and coatings accomplishes this, and is called the shell. It also can be done more simply with a looser fitting shell that can be snugged up with a drawstring and/or venting. That’s what they make zippers for.
There is a saying, “If your toes are cold, wear a hat.” Most places in the northern latitudes live by those words. It takes a lot of blood to even grow hair, which makes the scalp a great radiator. It is said that you lose as much heat from your head as the rest of your body combined. This isn’t precisely true, but the amount of heat loss is still impressive. Wear a stocking cap to trap some air, and a hood over it to seal it. That can be the difference between hypothermia and health.
Heat and cold illness share the illusion that you can push through them. Both are fundamental disturbances of the most basic life processes. Chemical reactions are all temperature dependent. Determination, or the often celebrated grit, has nothing to do with keeping you safe from too high or too low of a core body temperature. Prevention, anticipation and watching each other for signs of distress will often save the day.
Stay warm out there,
Dr. B
Donald Bucklin, MD (Dr. B) is a Regional Medical Director for U.S. HealthWorks and has been practicing clinical occupational medicine for more than 25 years. Dr. B. works in our Scottsdale, Arizona clinic.
Special populations need to take further consideration of extreme cold such as diabetics, especially those with neuropathy in the extremities, workers with prior frost bite exposure (neurologic damage to extremites), and cancer survivors with neuropathy secondary to chemotherapy.