If you sniff at the idea that aromatherapy can be therapeutic, guess what? Science doesn’t agree. One study found taking a deep whiff of lavender before a root canal can help prevent you from being a quivering mess in the dental chair. And research shows the scents of lemon balm, rosemary and peppermint can boost your mood and make you more alert in the morning.

One theory on why aromatherapy is so effective: The molecules that make up scents take a direct route from the smell receptors in your nose to your brain’s memory and emotion centers.

But if you're getting your aromatherapy by way of burning incense, science suggests you could be doing some damage to your lungs.

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Lighting up lung trouble

A 2008 study of more than 61,000 people in Singapore, where incense is often burned for religious reasons, found that incense users were at higher-than-normal risk for cancers of the respiratory tract, including lung cancer. Later research found this same group also had a 12 percent higher risk of dying of cardiovascular disease than those who didn’t use incense.

More recently, scientists from the University of North Carolina at Chapel Hill (UNC-CH) looked at the effects of burning incense on people in the United Arab Emirates. Of the people studied, 86 percent were exposed to burning incense at least once a week and 44 percent were exposed to it daily. The researches found burning aromatic incense was associated with inflammation in lung cells, as well as headaches, wheezing, difficulty concentrating and forgetfulness.

A sooty affair

According to Karin Yeatts, PhD, research assistant professor for epidemiology at UNC-CH, who was co-author of the United Arab Emirates study, incense can release soot and ultrafine particles into the air that can cling to cells in the lungs, leading to genetic changes that have been linked to cancer. Particulates from incense also can produce hazardous chemicals and organic compounds, including formaldehyde, carbon monoxide and hydrogen sulfide.

Incense generally gets its fragrance from aromatic plants and essential oils that aren’t in themselves dangerous. That changes when burning is involved.

Some incense sticks, like joss sticks, are made from a fragrant material. Other sticks consist of a slender piece of bamboo or wood that has fragrance added. Mosquito coils, available in supermarkets and hardware stores, are forms of incense with an insecticide added.

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Incense, candles and asthma

If you have a child with asthma (or you yourself have it), you may want to avoid incense and even candles. “Studies here have found children with asthma who live in homes where candles and incense are burned have more asthma symptoms,” says Yeatts.

Safer incense and other options

Occasional incense use probably isn't hazardous to most people, says Yeatts, but she says it's not recommended for those who have asthma or other lung conditions, such as chronic obstructive pulmonary disease.

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If you’re going to burn incense regularly, she says, “make sure you have good ventilation — keep a window open. Don't inhale dense smoke.” Or get your aromatherapy fix with an essential oil diffuser, which spreads fragrance as a vapor or mist — no matches required.

Denise Foley is a veteran health writer and a former contributing executive editor at Prevention magazine.