Susie Neilson

The U.S. has the worst rate of maternal deaths in the developed world.

When we smear on sunscreen, dermatologist Kanade Shinkai with the University of California, San Francisco says, most of us don't think about it getting under our skin.

"I think there was an assumption that these are things that we apply to our skin — they don't really get into our bloodstream," Shinkai says.

What if you could put a drop of water into a miniature laboratory — not much bigger than a smartphone — and find out whether the water contains the bacterium that causes cholera?

A simple test like that could help prevent outbreaks of the disease, which sickens as many as 4 million and kills up to 143,000 each year, mostly in poorer countries.

The ancient disease of cholera is spread primarily through drinking water that contains the bacterium called Vibrio cholerae.

Scientists don't know much yet about the long-term effects of "vape juice," the liquid used in e-cigarettes and vaporizers. But researchers analyzing the liquid and the vapor produced when it's heated say some kinds of e-liquids are reacting to form irritating chemicals called acetals while they're sitting on shelves.

Editor's note: This story has been updated to include comments from Juul.

Popular e-cigarette company Juul's November 2018 commitment to stop marketing its products to youth on social media may have done little to curb the brand's reach among young people.