It's one of the familiar smells of Asia, from the temple to the family altar, but the next time you are surrounded by a cloud of incense smoke you may want to hold your nose.
Research in Taiwan has lent credence to suspicions that the joss sticks and incense that are burned as offerings to the gods may get you to heaven far quicker than you'd like.
Medical professionals have long suspected that joss sticks and incense - usually containing a blend of plant extracts and oils - emit harmful fumes when burned. Now, researchers from Taiwan's National Cheng Kung University in Tainan say joss fumes contain particulate matter, gases and organic compounds that could be more harmful than tobacco smoke.
'On average, incense burning produces particulates greater than 45 milligrams per gram burned, as compared to 10mg/g for cigarettes,' says a report by Cheng Kung University's department of engineering.
Researchers studied the make-up and fumes from incense, joss sticks, cones and coils, and analysed smoke from a Taipei temple, which was found to contain high levels of compounds blamed for causing lung cancer.
Emissions levels were higher than at a city road junction. The toxins found are harmful to the lungs and can cause allergic reaction to the skin and eyes.
Lin Ta-chang, a spokesman for the Cheng Kung group, likens incense and joss-stick fumes to second-hand smoke.
'Pollutants emitted from incense burning in an enclosed environment are harmful to human health,' he says.
'While it is relatively difficult to directly study the effect of incense smoke pollutants on health, several epidemiological studies have suggested that they do cause health problems.'
Incense burning produces volatile organic compounds such as benzene, toluene and xylenes, as well as aldehydes and polycyclic aromatic hydrocarbons, the study found.
The scientists, who conducted their study research in 2008, noted that during some major ceremonies, hundreds or even more than 1,000 joss sticks are burned at the same time.
Britain's National Health Service, which reviewed the Taiwanese study, said: 'Smoke is smoke, and cigarette smoke is not the only type of smoke that is harmful.'
A multinational study in 2008 also found that exposure to incense fumes posed significant public health implications. Jeppe Friborg, of the Statens Serum Institut in Copenhagen, and colleagues in Singapore and the US studied associations between exposure to incense and a spectrum of respiratory tract cancers.
They sampled 61,320 Singaporean Chinese who were free of cancer and aged between 45 and 74 from 1993 to 1998, studying respondents' living conditions and dietary and lifestyle factors until 2005.
They found 325 upper-respiratory tract cancers - including nasal/sinus, tongue, mouth, laryngeal and others - and 821 lung cancers during the follow-up period.
The American Cancer Society said at the time that 'incense use is associated with a significantly increased risk of upper-respiratory tract cancer' although there was no overall effect on lung cancer.
'It also considerably increased the risk in 'never' smokers, which points to an independent effect of incense smoke.'
The Taiwanese researchers also cited a 1996 report in the journal Cancer that showed a high incidence of nasopharyngeal carcinoma in male Hong Kong patients who burn incense, compared with other malignant cases.
They found that 74.5 per cent of the nasopharyngeal cancer cases studied and 52 per cent of all other malignant cases were exposed to incense smoke, and concluded that incense smoke could be a factor.
Ko King-tim, an engineering professor at City University now in remission from the cancer, says the public must be aware of such risks although he doesn't link his disease with incense-burning.
'Most people are not aware of the causes of various cancers. Some are genetic, some are [linked to] substances or stress-induced,' says Ko, who created a website for people with nasopharyngeal cancer.
'Most people in Hong Kong are unaware of the early symptoms of different cancers. Awareness of these early symptoms could save a lot of lives,' he says.
'Air pollutants such as incense smoke or car exhaust fumes are hazardous to health, whether [they cause] cancers or other illnesses.'
Although various 'herbal' and 'natural' incense options are also sold on the internet, the Taiwanese researchers stopped short of calling for an end to the deeply rooted tradition of burning incense, with Lin recommending devotees 'keep the room well-ventilated' while they burn it.
'It will effectively dilute indoor air pollutants and hence reduce the risk of exposure.'
Incense sticks have a slender bamboo stick onto which the mixture of ingredients is attached, while joss sticks come without the stick. Stick incense is the most popular in temples in Asia.
While the exact content of incense sticks is a commercial secret, most are made from a combination of fragrant gums, resins, wood powders, herbs and spices, the report says.
A typical stick of incense comprises, by weight, 21 per cent herb and wood powder, 35 per cent fragrance material, 11 per cent adhesive powder and 33 per cent bamboo stick.