Blowing Out Birthday Candles Is Actually Really Gross


Blowing out the birthday candles and making a wish is a time-honored tradition, and is carried out no matter how young or old the person may be.

However, the transfer of bacteria may cause some to second guess the need for candles, as a new study reveals that with one blow, the amount of bacteria on birthday cake increases by 1,400 percent.

Credit: Dark Dwarf/Flickr, CC BY-ND 2.0

The study, authored in part by Paul Dawson and published in the Journal of Food Research, was used as part of a graduate studies program, enlisting the help of students in the quest to answer common questions regarding food safety and research. These students at Clemson University were both subjects and researchers in the study, simulating a birthday party to achieve the most similar results.

The only difference was that they did not use an actual cake, but instead utilized a base of styrofoam, covered with tinfoil and coated with cake frosting. The students even were given pizza prior to the experiment to simulate the salivary activity that would commonly occur at a birthday party. As Dawson told reporters, “we thought it might help the salivary glands get going.”

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They stuck candles in the faux cake, lit them, and blew them out, just like any birthday boy or girl would. However, the party ended there as they then examined the frosting to determine the spread of bacteria from the saliva in a single blow. The frosting from each “cake” was diluted with water and spread on agar plates.

Every single plate contained bacteria, but some contained much more than others. The average across all of the plates showed a 14 percent increase in bacteria. In one unusual case, the increase in bacteria jumped up to 120 percent.

“Some people blow on the cake and they don’t transfer any bacteria. Whereas you have one or two people who really for whatever reason… transfer a lot of bacteria,” Dawson stated. However, even with this massive transfer of bacteria via the saliva of the candle blower, Dawson still believes that there is not too much cause for concern.

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“It’s not a big health concern in my perspective,” he told reporters. “In reality if you did this 100,000 times, then the chance of getting sick would probably be very minimal.”

However, he does encourage people to use caution if the person blowing out the candles on their big day is sick, as those bacteria can carry a contagious illness. That being said, the majority of bacteria in a person’s mouth is ultimately harmless. The main point of this study is that the bacteria is there, and if that causes disgust or alarm, skipping the cake at the next birthday party might be for the best.