Children from homes with regular incense burning have a higher risk of developing asthma, according to a Taiwanese study that hints a particular gene variant could be involved.
Among nearly 3,800 middle-school children, researchers found 3% had current asthma and more than 5% had wheezing during exercise.
Kids whose parents burned incense were 36% more likely to have current asthma and 64% more likely to wheeze when they exercised.
Of the children, 48% carried no copies of a gene variant known as GSTT1, which helps regulate a family of enzymes that protect body cells from oxidative damage -including that caused by cigarette smoke or other toxic chemicals.
People without this genetic variant have been found to have higher risks of allergies and asthma. Similarly, such children in the Taiwanese study were 43% more likely than their peers who carried at least one copy to currently have asthma.
Very high risk of asthma
When the researchers looked at incense use in those children's homes, those with daily exposure were 78% more likely than those with no exposure to currently have asthma. That pattern was not true, however, of children with the GSTT1 gene variant.
The findings, published in the European Respiratory Journal, suggest that a combination of genetic susceptibility and exposure to incense combustion by-products may raise some children's asthma risk.
Incense has been used for millennia in many cultures' religious and spiritual ceremonies. In Asia, people commonly burn incense in their homes, a practice that is becoming more popular in Western countries as well.
Incense and other respiratory illnesses
Incense is usually derived from fragrant plant materials, like tree bark, resins, roots, flowers and essential oils. Past research has found that burning these materials can produce harmful substances, including benzene and polyaromatic hydrocarbons, and there is evidence that incense use might contribute to respiratory ills.
A 2008 study of more than 61,000 Chinese adults followed for up to 12 years found a link between heavy incense use and various respiratory cancers, including oral, nasal and lung cancers.
Neither that study nor the current one proves that incense is the reason for the heightened disease risks. However, these latest findings raise the possibility that limiting incense burning at home could help curb some kids' asthma risk, according to lead researcher Dr Yungling Leo Lee of National Taiwan University in Taipei.
Still, more remains to be learned about the potential incense-asthma connection. It is not clear, for example, whether the current findings can be generalised to other countries, Lee said.
The researchers noted that while some studies in Asian countries have found connections between incense burning and respiratory symptoms in children, others -including one of schoolchildren in Hong Kong have not.
Other researchers have pointed out that different types of incense might differ in relation to disease risk. In some Asian countries, for instance, people commonly use long sticks or coils of incense that burn slowly over an extended period -a pattern of use that could be a factor in any respiratory health effects.
According to Lee, it would be "interesting" for future studies to look at the relationship between gene variants, incense and asthma risk in children living in other countries.
(Reuters Health, Amy Norton, December 2010)