If you go outside on a cold day, the first thing you will hear from your mom and dad is a reminder to bundle up — often accompanied by these words of wisdom: “You need to wear a hat because you lose more heat through your head than the rest of your body.”

While this is not exactly true, wearing a hat on chilly days will definitely help you stay warm. Here’s how.

Warmblooded animals control their body temperature by balancing heat production (from cell function) and heat loss (to the environment). Cold surroundings do lots of sneaky things to steal the heat from your body. If you come in direct contact with a cold object, like sitting on a snowy hill, you lose heat conduction. (Conduction is the process that causes heat transfer when two objects are touching each other — in this case, the snowy hill and your butt.) If you come in contact with cold air, you lose heat through convection. (Convection is the process that causes heat transfer when a gas moves past an object — in this case, cold air moving across your skin.) There is even something called the “chimney effect” that can work against you. Dense, cold air works its way into your pants and sleeves and pushes warm, light air out through other openings. Wind also works through convection, which is why blustery, cold days are the worst.

If it’s cold outside, the brain directs a number of actions to keep your core temperature steady. The blood vessels in your skin contract (get smaller) to preserve heat. That’s why your hands and feet may become pale and cool in cold settings. By redirecting blood flow, the brain keeps your muscles and organs warm even though your hands, feet and skin become cold. You feel cold, which encourages you to put on warm clothes. If it’s really cold, you may even shiver, which increases heat production in your muscles.

Okay, back to hats.

As noted above, you lose heat from any part of your body that comes in contact with a cold environment. And the part of your body that is most often exposed to the elements during the winter is your poor defenseless head!

Here are some tips to keep the cold air (and your parents) off your back on chilly days.

Wear warm clothes.

Wear gloves and a hat. (If you hate hats, wear earmuffs.)

Wear windproof jackets on windy days.

Button your collar (or wear a scarf), and consider tucking your pants into your socks to prevent the chimney effect.

—Howard Bennett

Howard Bennett, a Washington pediatrician, is the author of “Harry Goes to the Hospital.”