So THAT'S Why Your Nipples Get Hard When It's Cold

When the temperature dips, out come the nips. Doctors explain what's happening in your body.

Exposure to cold temperatures can affect the body in a number of ways, like making your teeth chatter or cheeks redden. But have you ever wondered why nippy weather perks up your nipples?

It’s not just a winter phenomenon — it can also happen in warmer times of year, like when the air conditioning is on full blast. So what exactly is occurring in the body when nipples become erect?

The physiological process that leads to hardened nipples when cold is also what causes goose bumps (known medically as piloerections), dermatologist Dr. Joshua Zeichner told HuffPost.

“This response is beyond our control and is a result of our bodies’ automated reactions to the environment,” said Zeichner, an associate professor of dermatology at The Mount Sinai Hospital in New York City.

Essentially, a drop in temperature triggers your sympathetic nervous system, which is behind the fight-or-flight response and other involuntary bodily functions. This process activates specialized nerve cells controlling the erectile muscles that cause hard nipples and goose bumps, according to a 2016 study published in the journal Nature Neuroscience.