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Skip to 0 minutes and 6 seconds The art of creating perfumes dates back to Egyptian times. Perfumes were used to cover up unpleasant odours coming from unwashed bodies. In the 17th century, during the plague, doctors treating plague victims covered their mouths and noses with leather pouches containing pungent cloves, cinnamon, and spices, which they thought would protect them from disease. So, many naturally occurring materials have been used to make perfumes - ambergris, one of the most valuable raw materials in perfumery is produced in the intestines of sperm whales, while musk is secreted by the musk deer. So, using these natural materials, how do we create perfumes? And why was Chanel No 5 such a landmark fragrance? This video helps us to find out.

Skip to 0 minutes and 52 seconds Perfumers use names like composers use when writing music. For example, individual ingredients contribute notes to the overall composition and the notes are divided into head notes, heart notes, and base notes. The head notes, are often the more volatile materials, lower boiling components, that give the initial impact; the heart notes form the bulk of the perfume; and finally the base notes are higher boiling components that fix the more volatile components. When creating a perfume you need to get the right balance of head, heart, and base notes - the base notes should ensure that the head notes are not immediately lost. Head notes of natural perfumes often come from citrus oils, herbs and green foliage.

Skip to 1 minute and 37 seconds While heart notes are typically flower oils, including rose, geranium, lily and violet. Finally, the base notes are classically woody, musk and amber materials. Today, perfumes are manufactured more and more frequently with synthetic chemicals rather than natural oils. Less concentrated forms of perfume are also becoming more popular. This decreases the cost of the fragrances, leading to more widespread and frequent, often daily, use. A landmark example of a perfume is Chanel Number 5. In 1921, for the first time, Mademoiselle Chanel used volatile low-boiling aliphatic aldehydes, including 2-methylundecanal, as the head notes alongside natural oils including jasmine. The success inspired other perfumery houses to experiment with synthetic materials and the modern age of perfumery was born.

The notes of perfumes and the potential dangers of scented products

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 inside of 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.

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.

It became clear that limonene (a compound extracted from the rinds of oranges, giving a citrus scent, which is looked at in greater detail further along in the week) 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 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) 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.)


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. 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 house-plants might help to absorb the toxic methanal produced by fragranced products.

It is the dose which makes a 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!

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 = 6.4
Warfarin = 10
Methanal (Formaldehyde) = 600-800
Limonene = 5,300
Sucrose (Table sugar) = 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, 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 made from parahydroxybenzoic acid, 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.

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Exploring Everyday Chemistry

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