Is burning incense safe during pregnancy?

What does the evidence say about burning incense during pregnancy?

1. In a Taiwan birth cohort of term births, mothers who burned incense during pregnancy had babies with measurably smaller head circumference at birth, and boys also averaged lower birth weight, though the effect on girls' birth weight wasn't statistically significant. 1
2. In a cohort of nearly 65,000 mother-child pairs, being exposed to incense-burning smoke at least twice a week during the first trimester specifically was linked to the strongest increase in a child's later risk of obesity, more than exposure spread evenly across all three trimesters. 2
3. The same cohort found that exposure spanning all three trimesters was linked to a smaller but still measurable increase in childhood obesity risk, about 12% higher odds, compared with children whose mothers didn't burn incense during pregnancy, so both timing and frequency appear to matter. 2
4. Laboratory testing of incense products has found benzene at levels several times to over 80 times higher than WHO guideline concentrations, along with formaldehyde exceeding WHO short-term exposure guidelines and detectable toluene and styrene, both classified as reproductive toxicants. 3
5. In a general-population study in China, adults who burned incense at home daily had higher blood pressure and close to 40% higher odds of hypertension than non-users, in a clear dose-response relationship as burning frequency increased. 4

Is burning incense safe in each trimester?

• First trimester. Frequent incense exposure during the first trimester, at least twice a week, showed the strongest association with a child's later obesity risk in one large cohort study, which lines up with this being a sensitive window for fetal development generally.
• Second trimester. The same study found the highest risk when exposure continued through the first and second trimesters together, so this isn't a window where frequent, heavy use becomes lower-risk.
• Third trimester. Exposure that continued through all three trimesters was still linked to a measurably higher obesity risk in that cohort, though the association was smaller than for concentrated early exposure. Separate research in non-pregnant adults has linked frequent, daily incense burning to modestly higher blood pressure, another reason to keep it occasional rather than a daily habit in a closed room.