Blowing out birthday candles is fun, but your spit is the icing on the cake — quite literally.

Scientists say that puckering up and making a wish sends varying amounts of bacteria flying onto your birthday cake.

“Until recently, there weren’t a lot of studies on this or how your spit gets aerosolized when talking,” Trevor Craig,  a food safety expert and the corporate director of technical training and consulting at Microbac Laboratories, told Well and Good.

 “The formation of thin layers of fluids in the lungs, upper airways, and saliva in the mouth are all broken and expelled when you talk or blow air out of your mouth,” he continued. “Either way, it’s a lot more aerosolized liquid coming out of you than you think.”

Not only does the cake get a spray of the birthday person’s saliva — but the cake is iced with a layer of bacteria. 

“There are studies that show media plates designed for growth of bacteria exposed to someone talking and a control, and the change in bacterial growth is astounding,” Craig said. “They have done the same with food items, and it’s hundreds of percentages higher after someone blows on it.”

In 2017, a study published in the Journal of Food Research found that blowing out candles led to a 1400 percent increase in bacteria than not blowing out candles. 

While bacteria can make someone ill, spreading your saliva over your cake may be gross, but it’s not necessarily dangerous. 

 “Our bodies are full of bacteria and our mouth has a lot of it in there, but not all bacteria is going to make you sick,” Craig said. 

“In fact, we have a lot of good bacteria in our bodies that are important to how we live and survive,” he explained. 

While it’s “not terribly high risk in most cases,” people may want to be extra careful about spreading illnesses.

“I did think about it more during the height of COVID or during flu outbreaks, [and] when I’m trying to avoid getting sick during vacation or when I’m around immunocompromised people,” he said. 

While it’s safe enough to eat cake after someone has blown out candles, eating cake leftovers presents a greater risk. 

“That bacteria will just keep growing and populating on that cake; that makes the risk on it higher and most likely shortens the cake’s shelf life,” Craig explains.

Those seeking to serve guests a spit-free treat can also opt to blow out a candle on a single cupcake, he suggested.

Luckily for those who want to spit on their cake and eat it too, there’s a special device to help blow out birthday candles without the waterworks. 

A Virginia dad invented a way for kids to blow out their birthday candles without spraying saliva onto the icing.

Mark Apelt’s battery-powered Blowzee is activated when someone blows into it, activating a fan that’s supposed to put out the flames.

“The user’s breath is redirected away from the cake,” the Blowzee’s product description says.

With Post wires