Blowing out candles on a birthday cake is an age old-tradition used to celebrate another successful orbit around the Sun without dying. Not that we want to “ruin the party” so to speak, but this millennia-old custom is actually a fairly gross, saliva-spewing splurge of bacteria. 

Blowing out the candles on a cake could actually increase the number of bacteria settling on top of the icing by 1,400 percent, according to a new study by scientists from Clemson University in South Carolina.

In their rather succinctly named study, "Bacterial Transfer Associated with Blowing Out Candles on a Birthday Cake", published in the Journal of Food Research, scientists made a mock-up cake out of styrofoam wrapped in tin foil with candles placed on top. Participants were first made to smell and eat a slice of hot pizza to mimic the type of food and order you'd eat it at a birthday party, get the saliva glands going, and introduce potential bacteria in the mouth. They then blew out the candles. After that, the researchers collected the samples from the foil and placed them in bacteria-friendly agar plates. The experiment was repeated three times on separate days by 11 subjects.

On average, blowing out candles was shown to increase the levels of bacteria on top of the cake by 15 times.

Some of the candle-blowers were more guilty than others, it seems. As everyday experience will tell you, some people are just more spitty and produce more saliva – known as hypersalivation – than others. One participant’s candle-extinguishing technique increased the number of bacteria by 120 times.

“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,” food scientist Professor Paul Dawson, lead author of the study, told The Atlantic.

Although it all sounds mighty disgusting, a birthday party’s saliva-spraying spree is probably nothing you should lose sleep over. As the study authors note, bacteria is part of everyday life. A few potentially harmful germs could be present in party-goer’s spit, such as Streptococcus pneumonia and Staphylococcus aureus, however, they are not likely to be in quantities that will do you much harm. After all, people have probably been doing this for thousands of years and “death by contaminated cake” is still a very rare thing to see on a death certificate.

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

So there you go. It's probably not fatal, but if you were ever looking for an excuse not to indulge in cake without people rolling their eyes, this is pretty legit.