Blowing out candles on birthday cake is a disgusting tradition — here's the scientific proof

birthday cake candles

Your friend's birthday is going well — you're all gathered around singing, a colorful cake has been presented — when suddenly, it happens: She's asked to make a wish.

Normally, you'd happily join in the collective tradition of asking her to blow out the candles. Maybe not after learning about a a new study that shows that the mere act of extinguishing those flickering lights multiplied the bacteria on the cake by 1,400%.

Perhaps the song should really go, "Happy bacteria to you."

For the study, published this summer in the Journal of Food Research, a group of food scientists prepared two test birthday "cakes" made of Styrofoam which they then spread with real icing (vanilla, in case you were wondering) and decorated with exactly 17 candles. Before having volunteers blow out the candles on both cakes, they had all of them smell and consume a piece of hot pizza — "to simulate a meal-dessert sequence." Afterwards, they compared the amount of bacteria present on each cake surface, and then repeated the whole exercise three times — because science.

They found that the cake that had its candles blown out had, on average, 1,400% more bacteria than the cake whose candles had not been blown out, and the range of those microbes was 100 times greater.

"I personally will be aware of the health status of the blower and won’t blow out candles if I'm sick," Paul Dawson, the leading author of the study and a professor of food science at Clemson University, told Business Insider.

Still, it's important to keep in mind that in many cases, especially if everyone present is healthy, all those extra germs could be harmless. By and large, we're surrounded by germs — and plenty of studies suggest that's a good thing; it helps protect our immune systems from truly harmful pathogens like those that can cause disease. But if your birthday boy or girl is sick, you might want to reconsider tucking into that cake.

There's plenty of research to suggest that the droplets you sneeze, breathe, or blow out are large enough — and can travel fast and far enough — to spread the bacteria and viruses that cause strep throat and the flu, among others.

So the next time you're at a birthday party, be aware of your guest's health. If someone seems sick, it might be worth skipping out on the cake, or getting birthday cupcakes instead.

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