Buzz
Scents often go unnoticed in our daily lives. While we naturally favor pleasant aromas and avoid foul ones, there's a deeper story behind these smells.
Take the chlorine-like smell in swimming pools, for example—it’s not actually chlorine. Similarly, the aroma of a brand-new car can pose unexpected health risks. Dive into these 10 intriguing facts about familiar odors.
10. The Scent of Rain: Petrichor
Ever noticed that earthy aroma right before a rainstorm hits? That’s petrichor. Contrary to popular belief, it’s not the rain itself that creates this scent. Instead, it’s produced by actinobacteria.
Actinobacteria spend most of their time breaking down complex materials from decaying organisms into simpler substances. During this process, they release a by-product known as geosmin, an organic compound with a distinct smell.
When rain is on the way, actinobacteria ramp up their activity. They sense the rising humidity and increase the breakdown of organic matter, producing more geosmin in preparation for the rain. This geosmin is what gives us the familiar scent of petrichor.
As rain hits the ground, it releases geosmin into the air. This scent intensifies during heavy downpours and can even carry over long distances, letting people know rain is nearby and might soon reach their area.
9. Chloramine
That strong, pungent smell often associated with swimming pools isn’t actually chlorine—it’s chloramine. This compound forms when chlorine reacts with ammonia. Pool owners use chlorine to disinfect water, which then breaks down into hypochlorous acid (HOCl) and hypochlorite ion (OCl-), both effective at eliminating bacteria.
Hypochlorous acid frequently interacts with ammonia (NH3), resulting in compounds like monochloramine, dichloramine, or trichloramine. Among these, trichloramine is the most potent in terms of odor and is primarily responsible for the distinctive pool smell, though dichloramine can also contribute.
Ever wonder where the ammonia in pools comes from? It’s introduced through swimmers’ sweat, urine, and body oils. By showering before entering the pool, swimmers can significantly reduce the amount of ammonia they introduce, thereby minimizing chloramine formation.
Higher levels of chloramine not only intensify the pool odor but also indicate more germs and less available chlorine. To combat this, pool operators often increase chlorine levels to neutralize the smell and ensure the water remains sanitary.
8. Ethyl Mercaptan
In its natural state, liquefied petroleum gas (LPG) is both colorless and odorless. The unpleasant rotten egg or cabbage-like smell associated with it comes from ethyl mercaptan, a chemical added solely to help detect gas leaks.
Before ethyl mercaptan was introduced, detecting gas leaks was nearly impossible. This changed after a tragic incident on March 18, 1937, when a gas leak-triggered explosion devastated a Texas school, claiming the lives of 370 teachers and students.
The explosion caused a massive fire that consumed the school in an instant. Witnesses reported that the blast lifted the building into the air before it crashed back down. Out of the 500 individuals present, only 130 survived the catastrophe.
Following the disaster, regulations were enacted mandating the addition of ethyl mercaptan to LPG. However, this solution isn’t perfect. Some people cannot detect the odor, and in certain cases, the chemical can remain trapped in pipes, failing to signal a leak.
7. Trimethylamine Oxide
Many people dislike the strong odor of fish and avoid eating it, yet they have no issue handling live fish. This is because live fish don’t emit that sharp smell. The distinct fishy aroma comes from trimethylamine (TMA), a by-product of trimethylamine oxide (TMAO), which is naturally present in fish.
Saltwater fish contain higher levels of TMAO compared to freshwater fish, as TMAO helps them regulate salt intake in the ocean. This is why freshwater fish are less robust than their saltwater counterparts. Once saltwater fish are caught and die, bacteria and enzymes in their bodies convert TMAO into TMA, creating the strong fishy smell.
6. Coffee
While good food typically smells pleasant and bad food smells unpleasant, the same isn’t always true for coffee. Although coffee has an appealing aroma that even non-drinkers enjoy, its taste doesn’t always match its smell for everyone.
When food is cooked, baked, or roasted, new compounds are formed. Coffee is no exception. Roasting coffee produces over 800 compounds, with 20 primarily responsible for its unique aroma, though 631 compounds contribute to its overall scent profile.
As we sip coffee, its aroma travels to the back of the nose, activating what’s known as the brain’s “second sense of smell.” Humans possess two olfactory systems: the first detects external scents, while the second responds to internal aromas, such as those from food or drink.
Coffee’s aroma changes after we drink it because saliva absorbs 300 of the 631 compounds responsible for its distinctive smell. The remaining 331 compounds don’t produce the same pleasant scent, altering our perception of the aroma.
5. New Car Smell
The beloved scent of a new car is surprisingly hazardous, classified as air pollution due to volatile organic compounds (VOCs). These carcinogens can trigger allergies, headaches, and even birth defects, making the smell far more dangerous than it seems.
The new car smell originates from a blend of volatile organic compounds released by materials like plastic, vinyl, adhesives, and paints used in car manufacturing. These chemicals typically evaporate, but in the confined space of a car, they accumulate, creating the iconic scent.
The new car smell fades over time but often returns in warmer weather. To minimize exposure, new car owners are advised to keep windows open during hot days. Automakers recognize the risks of VOCs and are working to eliminate the scent. For instance, Toyota has switched to water-based adhesives instead of solvent-based ones to reduce VOC emissions.
4. Biblichor
The term “biblichor” describes the distinctive aroma of old books. A relatively new word, its inclusion in the English language is still pending. The scent of aged books varies—some resemble vanilla, coffee, or chocolate, while others are a blend of multiple aromas. Regardless, all these scents fall under the umbrella of biblichor.
This unique smell arises from the breakdown of chemicals in paper, primarily cellulose and lignin, which are present in all paper. Lignin, the same compound that causes yellowing in old books, degrades over time, releasing acids and eventually breaking down into cellulose.
The scent of old books can vary depending on the materials used in their production and the era they were made. Compounds like furfural and benzaldehyde (almond-like), vanillin (vanilla-like), and 2-ethyl hexanol (flowery) contribute to the aroma. Additionally, toluene and ethyl benzene add a sweet undertone to the overall fragrance.
While new books also have a unique smell, it isn’t referred to as biblichor. This scent comes from the paper, ink, and adhesives used in the bookbinding process, giving freshly printed books their characteristic aroma.
3. Seaside Smell
The calming scent of the seaside is a major draw for visitors, alongside the scenic views and gentle breezes. This fragrance is produced by bacteria breaking down dimethyl sulfide (DMS), which originates from dimethylsulfoniopropionate (DMSP), a compound created by phytoplankton in the ocean.
Bacteria consume DMSP, releasing DMS as a by-product. DMS is a crucial molecule globally, playing a role in cloud formation and enhancing savory flavors in food. Even trace amounts of DMS can significantly influence the taste of various dishes.
Birds are drawn to DMS because it signals an abundance of fish nearby. This is due to DMS being derived from DMSP, which is found in areas rich with phytoplankton. Since phytoplankton serve as food for certain fish, these fish tend to gather in the same regions.
2. The Smell Of Farts
No discussion of scents would be complete without mentioning farts. Their odor varies widely—sometimes they’re odorless, while other times, the stench is so overpowering it can clear a room.
Research shows that individuals with healthier diets often produce the most unpleasant-smelling farts. Proteins from sources like milk, eggs, and vegetables generate sulfur in the digestive system. Sulfur, the same compound responsible for the smell of rotten eggs, is also what makes protein-rich farts particularly foul.
While sulfur-rich farts may be unpleasant, they indicate a protein-rich diet. The body simply expels excess sulfur. Similarly, foul-smelling farts can result from carbohydrate fermentation in the gut, which produces methane, hydrogen, and carbon dioxide—gases notorious for their strong odor.
Foul-smelling farts can also result from constipation, which occurs when excess waste builds up in the body. In such cases, the person may experience continuous flatulence until they relieve themselves. The odor worsens if there’s a delay, as the trapped waste continues to ferment inside the body.
1. The Smell Of Freshly Cut Grass
The aroma of freshly cut grass is both unique and soothing to humans, but for the grass itself, it’s a different story. If grass could scream, it would, as the cutting process is stressful. Instead, it releases green leaf volatiles (GLVs), the compounds responsible for the familiar scent we enjoy.
When plants release GLVs, they activate their defense mechanisms to protect against bacteria and fungi that could infect the cut areas. They also produce chemicals to seal the wounds, much like how blood platelets form clots to stop bleeding in humans.
While cutting grass is harmful to the plant, it has environmental benefits, such as releasing oxygen-containing hydrocarbons. However, some studies argue that grass cutting contributes to pollution, making its environmental impact more complex.
