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I borrowed my brother's truck to get some lumber. My brother's a smoker and smokes in his truck. To compensate for the smoking, he has one of those Little Trees hanging from his rear view mirror, and at least nine more hanging from his steering wheel. They're peach scented. After about 30 seconds, with all the windows down, I started getting dizzy and felt like throwing up. I put them in the glove compartment, but I could still taste them in the air. Here are my questions: What's in these things? How many are too many?

– Derek, Edmonton

As the saying goes, if they told you what was in those Little Trees – or any other fragrance – they'd have to kill you.

"I can't tell you what's in them because it's proprietary information," says Susan Montague, a consumer relations specialist at Car-Freshner Corporation in Watertown, New York. "I can tell you that they're perfectly safe."

The formulas have been a secret since the company invented the iconic cardboard pines in 1954, when chemist Julius Sämman studied tree aromas in the forests of Canada and tried to come up with a mask for the smell of spoiled dairy in milk trucks, according to the company's website.

There are no ingredients listed on the packages and the recommendations are simple.

"Hang them from the mirror, we don't recommend weird uses of the product," says Montague, who says she's heard it all from callers to the company, but won't specify where else people have put them. "Oh no, I'm not going to give your readers any suggestions."

And how many is too many? As many as you can stand, the company says.

"We have leave it up to the consumer to hang as many or as few as they want," she says. "I'm one of those fragrance-sensitive individuals and I have just one."

In 2009, British artist Jack Williams hung 350 Royal Pine-scented Little Trees in a room for an art installation called "Forest."

"The smell can definitely induce headaches, which I've suffered from. I'm guessing because cars are smaller spaces with no real airflow, the trees would be way more intense," Williams, the son of a car salesman, said in an email. "When the smell is at its beautiful best, the scent totally hits you at the back of your throat."

In the age of scent-free offices, consumers aren't asking the company to tone down its odours.

"No, it seems they want them stronger and stronger." says Montague. "We have a couple of people who really like to smell our Black Ice outside their closed vehicles."

The Canadian Lung Association says the problem with scented products isn't necessarily the scents themselves but the chemicals that produce them.

"So many different kinds of things can be in a scent," says Chris Haromy, Respiratory Therapist and Certified Respiratory Educator with the Lung Association. "Generally, man-made things are more harmful, but some natural products are also irritating to the lungs."

Haromy says there are no long-term exposure studies for scents and doesn't recommend them for anyone with lung diseases like asthma or chronic obstructive pulmonary disease.

"I would not suggest adding an air freshener to a car, especially if you're smoking in it," he says. "There are already enough gases and particles in the air."

Car-Freshner says it follows California Air Resources Board (CARB) standards for smog-forming Volatile Organic Compounds (VOC) in air fresheners.

Health Canada and Environment Canada do not test automotive air fresheners, says watchdog Environmental Defense Canada. It says Environment Canada has proposed regulations to put Canada in line with California standards, but individual products still won't be tested.

The claims of safety are potentially thorny because fragrance ingredients are usually trade secrets, and it's tough to say how whatever is in them will interact with the hundreds of other chemical particles inside a vehicle, says Jeff Gearhart, Research Director for U.S. group Healthy Stuff.

'Trust us, we follow the regulations' shouldn't be the answer. I think these products need to have more information," Gearhart says. "You buy a tube of toothpaste and you get an ingredient list, it's accepted."

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