Goose bumps, cold ears, numb toes: Humans react differently to cold temperatures. Some common beliefs, including that heavier people are less susceptible to cold, are inadequate explanations for our differing responses.
Everyone reacts to the cold in a different way. Some people's ears freeze; others feel their hands go numb first. Freezing is an individual experience, confirms Joachim Latsch of the German Sport University in Cologne.
Every human has heat sensors in his or her skin. Some people may have more sensors in their ears, which measure the cold, while others may have more sensors in other parts of their bodies.
The overall number of sensors can vary, too. "Just like people may have different sized feet, some people have more, others fewer sensors," the expert told DW.
Internal warning system
Those sensors only register one temperature: those designed to warn the body about the cold don't react to it being too hot. But no matter where in the world people live, their body temperature is similar, no matter whether they're based in the Sahara or Greenland.
"Our body temperature is at about 36.5 degrees Celsius. It does vary a bit," Latsch said, adding, "It can be life threatening if the body's temperature exceeds 42 degrees or falls below 30 degrees."
In the latter case, our vital organs stop functioning properly, possibly resulting in unconsciousness, hypothermia or death.
Back in the furry old days…
That is why the human body sends out a warning signal as soon as its temperature drops.
Even a slight draft can result in shivering and goose bumps. Latsch said that is a relict of ancient times when humans still had fur. "All our body hair has a small muscle at the point where it sticks through our skin. When it gets cold, the muscle contracts and pulls up the hair."
In furry mammals this creates a layer of warm, insulating air - while today's fur-less humans end up with goose bumps.
Not enough fur?
There's another self-defense mechanism against the cold, Latsch said. "When the body realizes that there's a need for more warmth, the muscles start to tremble."
Our lower jaw, in particular, starts chattering quite quickly, as it is somewhat loosely attached to our head via two joints.
Putting on weight won't keep out the cold
When muscles tremble, the blood starts circulating more quickly, and we warm up.
For women, the importance of body temperature has an additional component: their bodies are designed to keep the inner organs - and with them, any unborn child - warm.
But muscle mass plays a role, too. On average, muscles make up some 25 percent of women's bodies and 40 percent of men's. People with more muscles feel less cold.
But it's wrong to assume that fat keeps us significantly warmer: Chubbier people may resist one, maybe two degrees lower temperatures than their skinny counterparts, Latsch says, but not more.
For those looking for ways to feel less cold, Latsch has a simple tip: "It's not about putting on weight - but rather moving more!"
Whether you like tattoos or not may be a matter of taste. It may be about fashion, or a thing of conviction. But the chemistry in tats is unambiguous, with experts warning some ink may cause cancer.
A new casting process has made it possible to create stronger and thinner steel alloys than before. It's thanks to collaboration between academia and industry. The team is up for the German Future Prize.
Donor countries have pledged $9.3 billion for a fund aimed at helping developing countries tackle the challenges of climate change. Officials hope a $10-billion target will be met in the coming months.
The planet is facing huge environmental challenges and although it’s controversial some argue curbing population growth could help. But UNFPA's Daniel Schensul tells DW controls won't achieve much in the short-term.