The recent TV program “Trust Me, I'm A Doctor” broadcast on Wednesday 13th January referred to the levels of limonene and formaldehyde in people’s homes. More specifically, it was implied that using candles and cleaning products with citrus fragrances increased the concentration of limonene. It was then proposed that through an unknown mechanism, this resulted in an increase in the concentration of formaldehyde. Limonene is a naturally occurring essential oil. The natural oil from orange peel contains 94% limonene. A typical citrus fragranced candle might contain 0.5% limonene, derived from pressed orange oil. If we take the conclusions of the program seriously, grating an orange or lemon is likely to be detrimental to health.
In the program there was a link made between limonene and formaldehyde levels. The BBC study was only carried out on 6 homes. All of the homes contained formaldehyde. This is because formaldehyde may come from many sources such as cooking, smoking, heating, consumer products and pressed wood furniture and building materials. In newer homes, the most significant sources are from the pressed wood e.g. laminate floors, chipboard etc.
Absent from all of the above is any mention of safety limits. All chemicals, including water, are dangerous at too high a concentration. For example, coffee contains about a 1000 chemicals, about half of which can cause cancer at a high enough dose. Coffee (and other foods) are considered safe because the dosage of the chemicals is well below safety limits. There was no mention within the BBC study as to the safety limits of formaldehyde. In fact the levels of formaldehyde observed were within what are considered to be safe limits. This agrees with other studies that have found that scented candles are safe1.
1 Human health risk evaluation of selected VOC, SVOC and particulate emissions from scented candles. Regulatory Toxicology and Pharmacology 69 (2014) 55-70