If you try to avoid fattening foods at birthday parties, this story may have you swearing off cake forever. It might have crossed your mind that when someone leans over to blow out their birthday candles, they’re spewing spit and germs everywhere, and you’d be right about that. According to researchers, blowing out birthday candles increases the amount of bacteria on a cake by 1,400%. 
Who wants some ice cream?
After gorging on pizza, researchers at Clemson University blew out candles on an iced chunk of Styrofoam and measured it for bacterial contamination. They literally frosted a piece of Styrofoam for the test. Isn’t science amazing?
To examine the bacterial contamination on the faux cake, they used sterile water to dilute the frosting, then spread it on lab dishes to see how many bugs would grow. 
How much nastiness was on the “cake” depended on who blew on it, they found. 
Professor Paul Dawson said:
“Some people blow on the cake and they don’t transfer any bacteria. Whereas you have 1 or 2 people who really for whatever reason… transfer a lot of bacteria.”
On average, the huffing and puffing increased the amount of bacteria on the frosting 15 times. One of the researchers’ saliva, however, increased it by 120 times.
As disgusting as that is, Dawson and his team say you don’t have to worry too much about eating a birthday cake that has been blown on. If it were truly dangerous, blowing out birthday candles probably wouldn’t be such a popular tradition.
“It’s not a big health concern in my perspective. In reality, if you did this 100,000 times, then the chance of getting sick would probably be very minimal.”
Unless, of course, the person blowing out the candles is sick. So just use your head. If the birthday boy or girl clearly has the flu and they blow out candles, don’t eat the cake.
 Fox News
 Live Science