The Stupid Question: Why Does Striking A Match Remove Toilet Smells?

Well strike a light!

Well strike a light!

You’ve heard this piece of advice before. To rid a bathroom of unwanted smells and avoid the humiliation of having other people know you just pooed, simply strike a match. It’s folk wisdom that this works.

But how? This was the question that troubled The Enthusiast during a recent editorial meeting. I was determined to get to the bottom of the matter. First poot of call: clueless idiots on the internet.

Many people believe that the offending odours are simply masked by the sulphurous smell produced by the chemical reaction that ignites the match.

According to Ezine Articles, “Lighting a match produces sulfur dioxide. This chemical is so strong that it hides most other odors from your noses for a short time.”

This exact sentence has been cut-and-pasted into various other online ‘getting-rid-of-toilet-smells’ how-to stories.

User “Marmaduke” from this parenting forum adds: “I read somewhere that it doesn’t actually absorb the odours, instead, the sulphur dioxide in the match head have a numbing effect on one’s sense of smell…either/or it works.”

Another school of thought is epitomised by WikiAnswers, which suggests that lighting a match “burns the gas caused by flatulation.” Indeed.

Yahoo! Answers user “I’ll tell my mommy!” concurs, writing: “The scent comes from methane gas which the match will gladly use for fuel. Remeber though that methane is heavier than our air, so it may be nessecary to move the match around the interior of the toilet bowl to removed all of the gas.”

The trouble with these online theories is that methane is an odourless gas. Yes, faeces and flatus do contain methane, but their offensive smell is caused by hydrogen sulphide (H2S), combined with methyl mercaptan (CH4S).

Time to turn to the popular science experts: Dr Karl Kruszelnicki and the Mythbusters team. Speaking on triple j two years ago, Dr Karl argued that the key to reducing odours is the way the combustion process releases charcoal – activated carbon – into the air. So candles will work just as well as matches to eliminate odours.

Activated carbon has a large surface area (routinely more than 500 square metres per gram) and a non-polar surface structure, so it attracts the H2S molecule via Van der Waals forces and captures it by chemisorption. Oxygen on the surface of the charcoal exchanges with the sulphur atom in the H2S molecule to produce water and, hence, neutralise the odour.

Charcoal’s ability to capture volatile organic compounds means it is widely used in air and water filtration systems, medically to reverse the effects of poison or pharmaceutical overdose, and in health preparations that can ease digestive discomfort. This Singaporean forum suggests reducing toilet odours by chewing charcoal tablets, as popularised by semi-mythic “Japanese ladies”. (“The Jap ladies are really advanced in their thinking.”)

However, a 2006 Mythbusters episode claimed to debunk the theory that matches neutralise offensive odours. The team isolated hydrogen sulphide and methyl mercaptan separately in small sealed flasks, in which they then set off matches by remote control. The Mythbusters found no difference in the concentration of either H2S or CH4S before and after lighting the match.

When they enlisted researcher John Hunt to actually smell – and rate – the offensiveness of each gas, he found the match ignition made no difference to his perceptions of H2S, but reduced the smell of CH4S by half. The Mythbusters concluded that the smell of the match being lit and then burning masks our perception of the odours, rather than the match neutralising the gases.

So who do you believe – them or Dr Karl?

Some commercially available products claim to do the same job as matches. Just A Drop reckons it can eliminate 98 per cent of odours (although there are statistical problems with measuring this claim) by creating a film on the surface of the toilet water that ‘traps’  odours beneath. The product is a mixture of eucalyptus extract and perfumed oil.

Though named after the practice of flushing midway through pooing, Courtesy Flush is a similar product to Just A Drop. It contains “active enzymes, including tea and bamboo leaf extracts”. Marketing itself to sufferers of chronic bowel disease, the company sponsors the Crohn’s and Colitis Foundation of America.

The website also has a panicky all-caps warning: “DO NOT PUT COURTESY FLUSH IN YOUR EYES. COURTESY FLUSH SHOULD NOT BE TAKEN ORALLY.” This makes us suspect that legal issues may have arisen in the past surrounding such practices.

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  1. Sam says:

    Im australian and i tried it once. It was a waste of time. You have to hold the phone really still to even try to get the camera to focus. I dont know one person that uses the codes. Its a telstra gimmick. So no. Australians dont use those codes. Never have and never will. They dont even print them anymore.

  2. Roy G Ruelas says:

    if you don’t have a match or means to mask or eliminate the odor–> close the door & don’t nobody go in for 35,45 minutes;)


  1. [...] actually appeared on one of the episodes of “Mythbusters”. Here’s one review:…This answer .Please specify the necessary improvements. Edit Link Text Show answer summary [...]

  2. [...] clear the smell of poop from a room is the old tried & true method: light a match!  There are various theories on why this works, but in our experience, it always works well.  Sure, you’re leaving the telltale odor of a lit [...]

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