Christmas decorations surround us gently and unobtrusively. They do not try to teach or explain. And yet they conceal a wealth of science – light without heat, scent without forest, snow without frost, and fire that burns under precisely defined conditions. In the following lines, we will therefore take a closer look at the chemical and physical principles that quietly govern these inconspicuous decorations, and show that even the soft light on the tree, the scent or the flame of a candle are the result of precisely defined and controlled processes.
The Christmas tree is silent, yet it communicates. It constantly releases molecules that are captured by our sense of smell. The tree actually speaks the language of chemistry – using volatile substances that spread through the air. The scent of a live Christmas tree is the result of the release of volatile organic compounds, mainly terpenes such as α-pinene, β-pinene and limonene3. These substances are part of the metabolism of coniferous trees and serve primarily as protection against pathogens and herbivores. Their concentration in the air depends on the temperature, humidity and physiological condition of the tree. The gradual loss of scent is due to the depletion of these low-molecular-weight compounds and the limitation of their further synthesis after the tree is cut down. The scent of a Christmas tree actually has a similar effect on the body as being in a forest. Some research suggests that inhaling these compounds can affect the nervous system, promoting a feeling of relaxation and reducing stress.
Artificial snow used for decorations or Christmas villages looks like a toy. Add water and a voluminous white mass appears. It is usually made from superabsorbent polymers, such as sodium polyacrylate. These substances have the ability to bind large amounts of water and increase their volume several times over. The same principle is used elsewhere – it is the basis for nappies, sanitary products and medical dressings. The same chemistry can serve both practical and aesthetic purposes.
Today’s Christmas lights shine “cold” – that is, without the heat of old light bulbs. You can touch them and feel nothing. Unlike old light bulbs, where light was produced by a glowing filament, LEDs convert electrical energy directly into light. Electrons move in a precisely designed material and their energy is converted directly into light. This is a controlled movement of electrons in a semiconductor structure.
The colours we perceive as warm, cool or colourful are not random. They are the result of the chemical composition of the semiconductor material. Each material has its own “energy bands” that determine what colour of light the electrons release when they move. It is thanks to the precisely defined composition of materials that LED lights can shine in different colours, be energy efficient and have a long service life.
Candles are one of the oldest forms of lighting and remain a symbol of peace and warmth to this day. Paraffin, a mixture of saturated hydrocarbons obtained from petroleum, is most commonly used in their production. A candle is essentially a combustible wick coated with solid fuel. When paraffin burns, an oxidation reaction takes place, producing heat, light, carbon dioxide and water. The wick’s role is to absorb the heat-melted fuel and then bring it to the flame so that it can burn.
In recent years, however, there has been increasing discussion about the ingredients and possible toxicity of burning candles. Some types of candles, especially cheap paraffin candles with synthetic dyes or fragrances, can release toxic organic compounds, including aldehydes and aromatic hydrocarbons. In higher concentrations, these substances can affect indoor air quality and have a negative impact on our bodies. The discussion therefore focuses on the choice of materials and the safe use of candles. Alternatives include beeswax or soy wax and natural essential oils. Although they burn more slowly, they produce less soot.
Why does the flame flicker? It is neither coincidence nor romance. It is a reaction that constantly seeks balance. Because combustion never proceeds completely evenly. A slight movement of air, a slight change in temperature or flow, and the reaction will speed up or slow down for a moment. Flickering is a visual manifestation of the constantly changing balance between fuel and oxygen.
Aroma lamps and diffusers work by releasing volatile aromatic molecules into the air, which we then perceive with our sense of smell. Have you ever wondered why we automatically drip essential oil into water? It is a well-thought-out chemical-physical principle. Most essential oils are hydrophobic – they do not dissolve in water. Water serves several functions here: it allows for the gradual and controlled release of oil molecules, disperses them into the air and reduces their concentrated power, allowing the scent to spread more evenly. “But how do we get these molecules into the air?”
Aroma lamps use the heat of a candle flame, which increases the kinetic energy of the molecules and accelerates the evaporation of the oil. Diffusers often work mechanically – ultrasonic vibrations or a small fan create an aerosol of water and oil that spreads evenly throughout the room, with evaporation taking place safely without an open flame.
The result, whether it is a lamp or an electric diffuser, is that aromatic molecules are released into the air and create a characteristic scent. Some scents come from natural sources, others are synthetic – chemically created to mimic a specific aroma. Interestingly, the nose cannot distinguish between “natural” and “synthetic“. The shape of the molecule is decisive. If it is the same, the scent is the same – regardless of its origin.
Just like Christmas baking or cooking, Christmas decorations also involve chemistry – quiet, precise and inconspicuous. In both cases, chemistry does not function as an abstract science, but as a silent mechanism that shapes our sensory perception of Christmas. Perhaps that is why Christmas feels so special. It is a time when science and emotion meet without competing with each other. You just need to look a little more closely.
Ing. Mária Zajičková, PhD.
organic chemist, science populariser
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2. McGee, H., On Food and Cooking: The Science and Lore of the Kitchen, Revised Edition, Scribner, 2004.
3. Mochizuki, M. et al., Volatile Organic Compounds from Conifers and Their Effects on Human Physiology, Journal of Chemical Ecology, 2017, 43(2), 101–115.
4. Pawlak, Z., Chemistry of Everyday Materials, Springer, 2019.
5. Sze, S.M., Ng, K.K., Physics of Semiconductor Devices, 4th Edition, Wiley, 2021.
