Why does cold fresh air help nausea go away?

Imagine you're driving down the highway, enjoying the start of a long road trip, when all of a sudden one of the children in your back seat moans, "I don't feel so good." Your immediate response, besides scrambling for a barf bag, would probably be to crack the windows to let in fresh air.

So why does cold air help get rid of nausea? 

"When trying to understand why fresh, circulating, or cold air seems to help alleviate symptoms of nausea, it's ideal to look at research related to motion sickness," Dr. Robert Glatter, an emergency physician at Lenox Hill Hospital in New York City, told Live Science in an email. People experiencing motion sickness often "seek colder temperatures or environments with improved air circulation, or choose options that cool our bodies down, when in fact the actual mechanism behind [nausea] involves a drop in our core body temperature," he said.

Related: What's the hottest temperature the human body can endure?

The hallmark symptoms of motion sickness are nausea, vomiting and sweating. Lesser known is that when a person gets motion sick, their core body temperature drops. They actually become slightly hypothermic. This phenomenon was first noticed about 150 years ago in sailors suffering from seasickness, but scientists began to study this phenomenon only in the last several decades, according to a study published in 2014 in the journal Temperature. 

Capillaries in the skin dilate during motion sickness, which allows more blood to flow through close to the skin's surface, losing heat to the environment and lowering core body temperature. This process goes hand-in-hand with breaking out into a sweat to further lower their body temperature, which a person may experience as a "cold sweat" since they're slightly hypothermic. 

When a motion-sick person's temperature drops, their central nervous system, specifically the hypothalamus, the part of the brain that regulates body temperature, tries to counteract the plunge. So although their core temperature is low, a nauseated, motion-sick person may actually feel hot and flushed.

This drop in temperature and the body's compensation reaction to it are actually what make a person feel nauseated, Glatter said. Getting cold air or placing a cool compress on the back of the neck or forehead for a few minutes can help reduce the feeling of being hot or flushed because it counteracts the hypothalamus' efforts to raise body temperature, thus easing the feeling of nausea.

Experts aren't quite sure why the temperature change associated with motion sickness occurs. One potential reason could be that at a lower temperature, tissues need less oxygen to survive, and it may be more difficult for a person to get enough oxygen when they're ill. However, it's "more likely an adaptive response influenced by poorly understood mechanisms at the cellular level," Glatter said.

Similarly, experts also aren't sure why the temperature drop and subsequent compensation to increase body temperature leads to nausea. One theory suggests that both the nausea and temperature change may be a natural way the body defends itself in response to toxins. Nausea often leads to vomiting, which can clear toxins from a person's system. So-called "defensive hypothermia" may also protect against toxins by conserving the person's energy so they can focus on fighting the invader, according to a 2016 review in the journal The Quarterly Review of Biology. 

"If we assume that the 'cold sweats' associated with nausea are a part of natural defense against poisoning or infection, lowering of body temperature after detection of a toxin could be part of an evolutionary approach that results in 'defensive hypothermia,'" Glatter said. According to the 2014 study, evidence that "defensive hypothermia" occurs during toxic shock in human and animal models supports this theory.

Originally published on Live Science.