“A lot of this is a mental switch,” Ms. Martin said. “We have to convince ourselves we can go outside in the winter and not die. Wear long underwear, dress in layers when you go out, and you can go for a walk with a friend.”

Clothing matters a lot, said Dr. Castellani. Plan for three layers. The base layer should be made of a lightweight moisture-wicking fabric. (Moisture, even from sweat, will make you feel cold.) Athletic apparel often is made with synthetic wicking fabrics, including polyester, nylon or polypropylene. Natural wicking fibers include silk or merino wool, a favorite of outdoor enthusiasts because it’s softer than regular wool. Don’t use cotton as your base layer in winter weather — it retains moisture. Add a second layer of fleece, merino wool or regular wool for insulation. Your outer layer, usually a winter coat, should repel wind and rain.

Don’t forget a hat. If you wrap your body in warm clothes but forget the hat, as much as 10 percent of your body heat can escape through your head.

Hands and feet also need special attention. Two sock layers can help, but loosen your shoes or buy winter boots a little larger so they don’t fit too tightly and restrict blood flow. For hands, mittens are better than gloves, because they trap more heat. And while many people use hand warmers to keep fingers cozy, studies show that keeping forearms warm (to increase blood flow to the hands) is the better way to keep hands from getting too cold. Don’t blow warm breath into your mittens or gloves — the vapor from your breath adds moisture and will end up making your hands colder.

Adding heaters to an outdoor patio or hosting a few friends in a well-ventilated garage can also take the chill off outdoor socializing. If you gather in a garage, wear masks, keep the time you spend together short, and leave the big garage door, as well as any additional windows, open to increase ventilation. “If you open the whole garage door, that sounds less risky, but it’s not no risk,” said Dr. Asaf Bitton, executive director of Ariadne Labs at Brigham and Women’s Hospital and the Harvard T.H. Chan School of Public Health. “It’s semi-enclosed, so the more ventilation the better.”

This fall, Sally Jacobs, 63, of Boston added heat lamps to her patio and hired an electrician to improve the wiring in her garage to accommodate several space heaters. When her adult children or close friends come over, everyone wears masks, and they leave the garage door and garage windows open. For New Year’s Eve, she’s planning to ring in 2021 with a few friends outdoors on her patio. Ms. Jacobs plans to limit the celebration to about an hour — long enough for everyone to raise a glass, make a toast and say goodbye to an awful year. Ms. Jacobs said she knew that preparing the patio and garage for winter socializing was “the only way I’d get through the season.”