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Bacterial Transmission Research Takes the Cake

Updated: May 6, 2019

Author Credit: Tess Devine-Hercus, WISE Promotions Officer



I’d like to start this blog post with an apology – I’m about to reveal some life-altering information that can’t be forgotten. Scientists from Clemson University have researched the bacterial transmission of blowing out candles on a birthday cake, and you won’t like the results.


Think about how many times you’ve blown out the candles on a birthday cake (Hint: if you take the year of your birth, and count up to 2019, you’ll have an approximate amount). Canadian researchers have found that, in blowing out the candles on your birthday cake, you were unwittingly sending your guests home with more party favours than a Wizz-Fizz and a Freddo frog in a ‘Finding Nemo’ plastic bag.


But what’s more important for you, though, is the number of birthday parties you’ve been to and eaten a slice of birthday cake. Luckily for ex-children of the gluten, lactose, or nut free variety, this is where a lonely memory of a plate full of fruit, amidst peers chowing through a slice of chocolate cake that once resembled Spider-Man, takes a turn for the better.


To carry out the experiment, researchers used a foam ‘cake’ as the base, and a circle of foil with 18g of frosting with 17 lit candles. 11 participants ate a slice of pizza to adhere to a typical party diet, then blew out the candles (their birthday wishes weren’t documented in the research paper). Control cakes were set up in the same way, but weren’t blown out, and the whole experiment was repeated 3 times. After collecting the frosting from all the cakes, and culturing the bacteria, the horrifying results came to light.


One of the cakes showed a transfer of 37,000 bacteria in one blow (that’s a lot of party gate-crashers!), compared to a maximum of 300 in a control cake. Not only did the number of bacteria increase by a factor of 15 when candles were blown out, but the variation in the bacteria on the cakes increased 100-fold.


An impacting factor not considered in this research could be the number of candles on the cake, which correlates directly with the age of the individual blowing out the cake. If there’s an assumption that the younger someone is, the more bacteria they are exposed to, to then transmit, then the question gets more complicated by the fact that the force of their exerted breath may be lower because of their lung capacity and the lower number of candles they must blow out. (And that’s not even considering the likelihood of spit flying!)


If this is all very shocking to you, try asking for a slice of cake before the candles are blown out (I’d love to hear the response you get). Alternatively, just sing along to ‘Happy Birthday’, wildly out of tune, accept a slice, and call it an exercise for your immune system.


If you’re keen to hear more of this real, applicable, useful science, then the same researcher, Paul Dawson, published a book late last year called ‘Did You Just Eat That?’, including some myth-busting of double-dipping and the five-second rule.


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