Health Risks of Perfumed Chemicals

Extensive use of air-fresheners and body sprays, mixed with the decreased airflow of increasingly insulated homes, and the closing of windows in colder months, results in a heavily fragranced atmosphere. The regulation of perfumed chemicals within these products is strict but, once outside of the bottles, these chemicals have the possibility of reacting in the air, resulting in quite a nasty mix.

Air Quality in Homes

Studies undertaken by scientists at the National Centre for Atmospheric Science at the University of York have been used to test the air quality inside a selection of homes to determine the most abundant fragrance compounds, as well as any toxic molecules, resulting from the use of fragranced products. During the study, the levels of ‘volatile organic compounds’ (also known as VOCs) were measured. VOCs are organic compounds that can easily turn into gases or vapours.

Limonene Prevalent

It became clear that limonene (a compound extracted from the rinds of oranges, giving a citrus scent, was the most abundant compound, especially in the houses that used the most cleaning products and scented candles; in some cases, reaching over 30 ppbv (parts per billion by volume) – some of the highest levels the scientists had ever recorded.

Limonene + Ozone = Methanal

Limonene (C₁₀H₁₆) itself is not a major cause for concern (it is even used in food flavouring) but, back in York, it was determined that for every two molecules of limonene that are exposed to ozone – a compound found in air – one molecule of methanal (or formaldehyde, H₂CO) can be produced; with results confirming the correlation between limonene and methanal values. (Interestingly, many people associate ozone with just being in the stratosphere, but is also present at ‘ground’ level – it is produced in various ways including from electrical equipment such as photocopiers and from motor vehicle exhausts.)

Dangers of Methanal

Links have been found between inhaling methanal and cancer and, in 2011, methanal was listed as a human carcinogen. Long-term exposure to methanal and volatile organic compounds (VOC) in indoor environments may cause a number of adverse health effects including asthma, dizziness, and respiratory and lung diseases. So, the presence of methanal in our homes could be quite worrying. It is also noted that methanal is a byproduct of combustion (when burning natural gas, kerosene, gasoline, wood, or tobacco, methanal is produced) and so, in the home, tobacco smoking is another source of the chemical in the indoor environment.

Research will help inform housing design to improve indoor air quality using, for example, appropriate building materials and household products. While the easy solution to this problem would be to open windows and doors, another answer could be found using houseplants. A further study undertaken at York showed that houseplants do not have a significant effect on the levels of limonene present in the air in our homes, but that methanal levels are reduced in their presence. This suggests that houseplants might help to absorb the toxic methanal produced by fragranced products.

Dose Makes Poison

If you’re speaking about chemicals in the atmosphere, in foods or drinks, or anything, the most important principle is that the dose makes the poison (or toxin). Everything that we can consume or breathe is potentially toxic, but the most important thing to consider is the dose. For example, take the chemical Warfarin. In low doses it is used clinically to prevent blood clots after a stroke or heart attack, while it is used in high doses as a rat poison.

Coming back to methanal (or formaldehyde), typically, low concentrations of methanal are present in our body and it is the product of a healthy digestive system. It is also present in very low concentrations in a flu vaccination (it is used in the manufacturing process to kill or ‘inactivate’ the virus by cross-linking proteins in the virus so it can’t cause illness). A flu shot can include up to 100 micrograms of methanal, but our blood naturally contains 13,000 micrograms. Also, 100 micrograms represents just 0.83% of the amount of methanal in a pear!

Lethal Dose (LD50)

A commonly used measure of toxicity is the lethal dose, or LD₅₀, which is the estimated dose required to kill 50% of a group of experimental animals (the lower the value, the more toxic the chemical). For example, on oral administration in rats, the following LD₅₀ values have been reported (quoted in mg/kg):

Sodium cyanide (NaCN) = 6.4
Warfarin (C₁₉H₁₆O₄) = 10
Methanal (Formaldehyde, CH₂O) = 600-800
Limonene (C₁₀H₁₆) = 5,300
Sucrose (Table sugar, C₁₂H₂₂O₁₁) = 29,700

These values are often used as a general indicator of the toxicity of chemicals, but it is worth noting that the absolute values can be unreliable – they can vary between testing facilities due to factors including genetic characteristics of the sample population, the animal species tested, environmental factors and mode of administration.

Also, there is a variation between species – what is relatively safe for rats may be extremely toxic for humans. For example, whereas chocolate is comparatively harmless to humans, it is more toxic to many animals including dogs. The principle toxic ingredient in chocolate is a chemical called theobromine (C₇H₈N₄O₂), which has a LD₅₀ value of around 300 mg/kg in dogs and 1000 mg/kg in humans – this means a typical adult human (80 kg) would need to eat around 5.7 kg of unsweetened dark chocolate to be at a toxic level. That is a lot of chocolate!

Also, you may have come across parabens (or parahydroxybenzoates). Parabens are a family of compounds made from parahydroxybenzoic acid (C₇H₆O₃), which occurs naturally in many fruits and vegetables, like blueberries and carrots. Their use as preservatives in a variety of products, including cosmetics, is a very interesting and controversial topic.

A scientific review of cosmetics and their cancer risks published in 2018 in the JNCI Cancer Spectrum journal concluded that there is no evidence to suggest that using paraben-containing products leads to an increased risk of cancer. In contrast, studies with rats have demonstrated that parabens could cause breast cancer – but only after the animals were dosed with much higher levels of parabens than what we typically encounter. Once again, this shows the importance of the dose.