Here’s what happens to your body in subzero temperatures

The National Weather Service issued a windchill warning for Boston starting from Friday morning through later on Saturday.

Officials and health experts are urging New England residents to take safety precautions against the cold to stay safe as the windchill is expected to be as low as 30 to 45 degrees below zero.

But how exactly can the cold hurt your body? Here’s what doctors have to say.

How the cold weather affects your body, according to health experts.Adobe/Globe Staff

Frostbite

Experts say the most common injuries are frostbites and thermal burns on skin exposed to cold windchill, especially in subzero temperatures.

Dr. Matthew Mostofi, associate chief of emergency medicine at Tufts Medical Center, said that it can take as little as 20 to 30 minutes for frostbite and blistering to occur. After 30 minutes, cells injured by the cold temperatures can become irreversibly damaged.

“The colder temperature, the more rapid [a thermal burn] occurs when temperatures are below zero,” Mostofi said.

Fingers and toes chill the fastest as the body will prioritize conserving heat to important organs during periods of extreme cold, according to Mostofi. In extreme circumstances, this can result in the loss of digits and limbs.

Dr. Brian Yun, vice chair of clinical affairs in the department of emergency medicine at Boston Medical Center, said the wind can also increase the risk of frostbite during cold weather.

“It’s not only the temperature, but it’s also the wind,” Yun said. “When you combine those two, that will calculate the risk of frostbite.”

However, the harms of cold exposure extend beyond just frostbite.

Effects on lungs

Dr. Shruti Gohil, an assistant professor of infectious diseases at the University of California, Irvine, said breathing in cold, dry air can constrict upper airways. While this can cause coughing and wheezing, it also disrupts our systems for keeping viruses out of the lungs.

“The little hairs in the trachea, [or] your windpipe, get kind of frozen,” Gohil said, preventing them from catching and clearing out viruses, and bringing down the lungs’ immunity.

She added that spending more time indoors in the cold can also lead to infections as viruses transmit more easily in closed spaces.

“Your whole body’s immunity also needs sun exposure,” Gohil said. “And our immunity can also go down during those time periods [indoors].”

Risk of heart attacks

Gohil said that cold temperatures can create the shunting of blood as blood moves from one area to another in a pattern that isn’t normal. This is because of the body attempting to conserve heat for the vital organs, but also wanting to redistribute blood back out of the heart vessels to other parts of the body.

“When you have an underlying blockage, when all of this shunting is going on, you can end up creating more work for your body,” Gohil said. “So your heart starts to work a little harder.”

As a result, the shunting of blood can cause increased blood pressure and the risk of heart attack.

Yun said while cold temperatures by themselves don’t necessarily cause heart attacks, it’s when people physically overexert themselves during cold weather that creates cardiovascular problems.

“The silver lining to the cold weather [this week] is at least there’s no snow,” Yun said. “When people are shoveling snow, we do see a rise in patients who come in with chest pain or heart attacks.”

Joint pain

Some also say that cold temperatures can exacerbate joint pain, especially for those with arthritis.

Mostofi said while the cold’s relationship with exacerbating arthritis pain isn’t confirmed, there is a possibility that there could be a connection between the two.

“There are a lot of people who know when it’s going to be cold out because their knuckles start to hurt, so I don’t believe that it’s just random,” Mostofi said.

Gohil said that because joints are areas of the body that also have less circulation, cold temperatures can cause some people to “feel their arthritis kicking up.”

Stay safe

Other than bundling up and covering skin when going outside, Yun advises Boston residents to check on their neighbors and use safe heating sources.

“What people shouldn’t do is use their ovens to try to stay warm,” Yun said. “And we certainly do see a bump in carbon monoxide poisoning because of using heating sources that are not safe.”

Yun said it’s important for residents to be careful during extreme weather and to not underestimate how quickly the negative effects can come on.

“Make sure that you’re covering and also layering before going outside,” Yun said. “Do not underestimate how quickly frostbite can develop when it’s so cold.”