How Germy Is a Birthday Cake After Someone Blows Out the Candles?

Maybe back up a little so some of the germs might miss the cake?. Romrodphoto/Shutterstock

What if you sat down to dinner and your waitress blew with gusto across the top of your meal before placing it front of you? Gross, right?

That's what happens with birthday cake. We light some candles, sing a lively song, and the honoree sprays microbe-laden saliva all over the frosting in a happy attempt to douse the flames. Then we eat up, mostly oblivious to the germs we've agreed to share.

We've all been to kid parties where other wee party guests join in to help blow out the candles. That results in gobs of giddy spit flying in all directions, landing in puddles on the frosting. Some people will draw a line, refrain from cake and just have ice cream.

But what about a birthday cake with a normal amount of blowing out candles?

Researchers at Clemson University wanted to see how many germs you're likely to ingest when you have a piece of cake after the candle-extinguishing tradition. Their results were published in the Journal of Food Research in the aptly titled study, Bacterial Transfer Associated with Blowing Out Candles on a Birthday Cake.

The birthday cake experiment

Instead of buying real cakes, the researchers took Styrofoam, covered it in foil and slathered on frosting. Then they poked candles through the frosting into the fake cakes. Before volunteers blew out the candles, they ate pizza, so it seemed like the real deal and less of an experiment.

“We also wanted to simulate a birthday party,” study co-author Paul Dawson told the Atlantic. “We thought it might help the salivary glands get going.”

After the candles were snuffed, the frosting was removed so they could wait to see how much bacteria would grow.

The researchers found that blowing out candles resulted in 15 times more bacteria on the cake than when candles were not blown out. "Blowing out the candles over the icing surface resulted in 1,400 percent more bacteria compared to icing not blown on," the study found. But it varied from blow to blow, as some people seemed to transfer more germs than others.

“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 said.

So what's a partygoer to do? It's hardly a birthday if you have to skip the cake.

For his part, Dawson, a Clemson professor of food safety, isn't all that worried.

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

Still not convinced? This guy came up with a solution: Instead of blowing out your candles, try waving them out.