Table 2.

Health impact of incense-smoke constituents

	Source/features	Impact on human health	Reference
Carbon monoxide (CO)	Incomplete combustion of hydrocarbons, wood, incense, cigarette, and fossil fuels	Reduces oxygen-transport ability of blood by forming carboxyhaemoglobin. Even low-level inhalation causes dizziness, headaches, weakness, and nausea. High concentrations can cause severe illness.	[7]
Sulphur dioxide (SO2) and nitrogen dioxide (NO2)	May form complex compounds with other pollutants	Reduced work capacity, elevated cardiovascular complications, pulmonary impairment, respiratory illness, lung irritation, and perturbation in self-defence	[8]
Volatile organic compounds (VOCs)	Chemicals with low boiling points, evaporate easily at room temperature, and include benzene, xylene, toluene, and isoprene	Ophthalmic inflammation, nose and throat irritation, nausea, vomiting, headaches, asthma exacerbation, dizziness. Chronic exposure leads to cancer, liver damage, and central nervous system damage	[8,9]
Aldehydes	Generated by combustion of organic fractions, burning incense generates aerosols, formaldehyde, acrolein, and acetaldehyde	The chief VOCs are distinguished by their irritant effects, low molecular weight, and halogenated aliphatic and unsaturated aldehydes. They affect nasal mucous membranes and oral passages, causing burning sensation, bronchial constriction, and coughing. Exposure to formaldehyde aggravates the risk of cancer and impaired mucociliary clearance. Studies have reported that wood dust and formaldehyde exacerbate nasal cancer risk.	[7]
Polycyclic aromatic hydrocarbons (PAHs)	Strongly associated with incense burning, as revealed by studies on Taiwanese temples, Swiss churches	Indoor air had nearly 27 times the PAH extent of outdoor air in a temple study. A Swiss study also revealed PAH prevalence in sedimented dusts generated on incense burning.	[10,11]
Diethylphthalate (DEP)	Extensively used as perfume binder in Indian incense, may be emitted in the air on burning	Natively a plasticizer and detergent base, DEP is a potential carcinogen. Sprague Dawley rats fed 50 ppm DEP and 55 ppm ethanol showed altered lipid and enzyme expression in the liver and serum over 120 days. DEP alone severely impaired lipid metabolism, accompanied by liver toxicity.	[12]
Particulate matter (PM)	On the basis of penetration depth into the respiratory system, particles of <2.5 μm and 0.1 μm diameter are referred to as fine and ultrafine particles.	Can go as deep as alveoli, posing severest health risks. Incense burning generates four times the PM of cigarettes and is associated with multiple respiratory complications, including lung dysfunction and enhanced oxidative stress by initiating and propagating random reactions.	[1,13]