Smoking e-cigarettes delivers cancer-causing chemicals that get into the body — and popular fruity flavors appear to be the worst, researchers reported Monday.
They said teenagers who try vaping are poisoning themselves with many of the same chemicals that make traditional cigarettes so deadly.
Tests on teenagers show that those who smoke tobacco-based cigarettes have the highest levels of these chemicals in their bodies, but those who vape e-cigarettes also have higher levels of the cancer-causing chemicals than nonsmokers, the team at the University of California, San Francisco found.
"The presence of harmful ingredients in e-cigarette vapor has been established; we can now say that these chemicals are found in the body of human adolescents who use these products," they wrote in their report, published in the journal Pediatrics.
E-cigarettes use a device that delivers fluid laced with nicotine and flavors, creating a smoke-like haze.
They're promoted as a safer way to use tobacco — e-cigarette use is called vaping — and as a way to quit smoking. But public health groups, the surgeon general's office, and the Centers for Disease Control and Prevention worry about evidence that vaping can get teens addicted to nicotine, and will lead them to smoking cigarettes.
Many studies support the theory that kids who vape are more likely to go on to use other tobacco products, but there hasn't been much hard evidence about how directly dangerous e-cigarettes are.
Monday's study shows vaping delivers harmful chemicals and potentially harmful chemicals.
RELATED: 6 most unhealthy American workplace habits:
6 most unhealthy American workplace habits
6 most unhealthy American workplace habits
Americans work crazy long hours
Perhaps the most notorious habit of American workers is their tendency to work long hours.
A Gallup report from 2014 estimated that the average full-time worker in the United States works 47 hours a week, one of the highest figures in the world, and significantly higher than the rates in Western Europe.
For example, in Europe, the Working Time Directive gives employees in the European Union the right to work no more than 48 hours a week. In practice, employees in some countries, like Germany and Sweden, work closer to 35 hours a week, according to Cary Cooper, an American-born professor at Manchester Business School in the United Kingdom.
"Europeans see that as being inefficient," Storti told Business Insider. "They say, 'You should have finished that in the allotted time.'"
They hardly ever go on vacation
Vacation time varies from country to country, but Americans seem to get the short end of the stick, with most companies offering around two weeks of paid leave a year.
And what little vacation time Americans do receive, they don't always take advantage of.
According to the careers website Glassdoor, the average US employee who receives paid vacation only actually takes 54% of the allotted time each year.
Compare to that to a country like Sweden, where workers get five weeks of paid vacation a year, and it's no surprise that they reject the American system.
"American companies aren't looking at the evidence of the important of holidays, in terms of productivity afterwards," Cooper told Business Insider, who said burnout was a much bigger problem in the US than in other places. "You can't continue to work without many breaks during the year."
And they barely take any family leave, either
The United States doesn't guarantee any paid leave to new parents, instead leaving it up to individual employers.
The result is new parents take far less time off after having a child than other parents around the world. That's largely due to cultural stigma — women can be seen as prioritizing home life above all else, while men can be seen as being less serious about their careers.
But it's not that way everywhere. In Finland, for example, expecting mothers can start their leave seven weeks before having a child, and can continue for 16 weeks after the birth. Men in Finland are offered eight weeks of paid leave.
Americans tend to eat at their desks
Americans have a reputation for being chained to their desks, and the statistics seem to back it up.
A 2015 survey found that only one in five Americans actually spends their lunch break away from their desks, with most eating their midday meal while they continue to work.
On top of that, millions of Americans are skipping lunch altogether to continue working.
Meanwhile, in France, Spain, Greece, and other countries, lunch breaks can last an hour or more — and rarely take place in front of a computer screen.
Americans seldom take breaks during the day
Even outside of lunchtime hours, American workers rarely step outside for a break.
Meanwhile, in Sweden, workers often enjoy a daily breather called fika — an extended coffee break during which employees can gather and socialize. Many offices offer two breaks, one in the morning and one in the afternoon.
Studies have shown that taking breaks throughout the day help us increase creativity, regain our focus, and retain information.
And they send emails after work hours
One of the worst American work practices, in the eyes of foreigners, is the tendency to send and answer emails after work hours have ended.
In other cultures, there is more of a distinction between work life and personal life, and the two rarely bleed into each other, Storti said. And France took that to extreme measures, enacting a measure earlier this year that allows employees to ignore work-related emails sent after working hours.
"In Europe, they give 100% from 9 to 5. When they go home, that's it, they're finished. They resent being contacted late."
The same goes for weekend emails — even ones that are sent without the expectation the recipient will respond right away.
"When they come in Monday and see you emailed them on Sunday, they're going to be annoyed by that," he said. "The perception is Americans, they don't stop working."
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Dr. Mark Rubinstein of UCSF's Division of Adolescent Medicine and colleagues tested 67 teenagers who vape and compared them to 16 teens who both vape and smoke tobacco cigarettes and to 20 teens who do not use either type of cigarette.
They tested their urine and saliva and asked questions about cigarette use.
Those who used both types of cigarette had significantly higher levels of dangerous chemicals, including acrylonitrile, acrolein, propylene oxide, acrylamide and crotonaldehyde, the team reported. And those who used only e-cigarettes had much higher levels than those who used neither product.
"Among our e-cigarette-only participants, the use of fruit-flavored products produced significantly higher levels of the metabolites of acrylonitrile," they wrote.
"Acrylonitrile is a highly poisonous compound used widely in the manufacture of plastics, adhesives and synthetic rubber," the National Center for Biotechnology Information says on its website.
Acrolein "is toxic to humans following inhalation, oral or dermal exposure", the Environmental Protection Agency says. Some studies show it can play a part in bringing about lung cancer although the EPA says there is not enough data to show whether it causes cancer in people.
Teens are vaping more often than they are smoking cigarettes, the CDC says. The latest report on teen smoking shows 20 percent of high school students have used at least one tobacco product recently — mostly e-cigarettes. In 2016, 11 percent of high school students had used an e-cigarette in the past 30 days at the time of the survey — the CDC's definition of current use.
"Teenagers need to be warned that the vapor produced by e-cigarettes is not harmless water vapor, but actually contains some of the same toxic chemicals found in smoke from traditional cigarettes," Rubinstein said in a statement.
"Teenagers should be inhaling air, not products with toxins in them."
RELATED: 20 mistakes that are making your home unhealthy:
20 mistakes that are making your home unhealthy
20 mistakes that are making your home unhealthy
1: Not Keeping a Barrier Between You and Your Bedding
Use zippered dust-proof casings for pillows and mattresses. The pore space of such casings is so small that dust mites and their waste products can't get through.
2: Vacuuming Without a HEPA Filter
Use HEPA (high-efficiency particulate air) filters to prevent tiny particles of dust from being blown back out into the air.
3: Forgetting to Change the Vacuum Filter
Changing the filter is an essential part of keeping dust out of the air and preserving the life of the machine. Change the filter once it's showing wear and tear or every six months if you're using a HEPA filter.
4: Forgetting to Change the AC Filters
Never run your heating or air conditioning system without filters, and be sure to change them at least every three months.
5: Not Ventilating Your Bathroom
Running the exhaust fan (and making sure it's vented to the outdoors) helps remove moisture from this naturally humid room.
6: Not Attending to Your Gutters
Leaky gutters can cause excessive moisture to enter your basement or crawl space. If you don't have covered gutters, frequent litter removal is a must year round.
7: Too Many Textiles in the Bedroom
Carpeting, rugs, pillows, upholstered headboards and chairs are all dust catchers. Consider minimizing furnishings for an easier-to-dust environment.
8: Too Many Textiles in Your Living Area
The living room is the same as a bedroom. Keep upholstery to a minimum to reduce the amount of dust mites.
9: Inviting Allergens Into Your Yard
Avoid plants that are wind-pollinated — grasses are among the worst pollen offenders.
10: Not Following Your Nose
If you detect a musty smell in your home, inspect closely until you find the source of the smell. The sooner you find the mold, the easier it will be to remove.
11: Not Organizing Your Home Office
Clutter can harbor a plethora of dust mites — this includes stacks of papers, old magazines and office equipment. File paper inside a cabinet to stay organized and keep dust away.
12: Wearing Shoes Inside the House
Not only is wearing shoes indoors a health risk, but it can also increase allergens. Wet leaves bring in mildew and pollutants from grass get trapped on the bottom of shoes. Take your shoes off outside, or put them in a washable tray as soon as you walk in the door.
13: Letting the Trash Pile Up
You could attract some unwanted guests (like mice and roaches) inside your home if you let your trash pile up. Their droppings can worsen your allergies, so make sure you stick to a routine of taking out the trash.
14: Displaying Houseplants
You may enjoy your beloved fern, but houseplants encourage mold growth. Mold spores live in warm, wet dirt, so limit the amount and time you display them.
15: Letting Your Pet Sleep in Your Bed
Your favorite part of the day may be snuggling up to your fur baby, but pet dander traps allergens — which means you're inviting those allergens to your bed. If you can't resist the cuddles, then you should completely shave your dog. Just kidding — just be sure to bathe them once a week.
16: Keeping the Temp Too High
Dust mites and mold love to live in warm climates. Keep your thermostat around 70 degrees to help keep them at bay.
17: Installing Wallpaper in the Bathroom
Patterned wallpaper is a beautiful addition to any room, but installing it in wet rooms (bathrooms and kitchens) can increase the risk of mildew. Opt for tile or textured paint that's mold-resistant.
18: Not Using the Exhaust Fan When Cooking
If you love cooking, all that steam from the stovetop will produce excess moisture. Turn the exhaust fan on to reduce it, helping to decrease the chance of mold.
19: Ignoring Your Bathmat
Think about it. You step onto your bathmat completely wet on the daily. To keep it fresh (and to keep mildew away), hang it to dry after every use, and stick it in the washer once a week.
20: Avoiding Protective Wear While Gardening
Even if you aren't highly allergic to pollen, it can still irritate your eyes, nose and throat. To prevent this, always wear a mask and gloves while working in the yard.