Hygiene can be, well, ambiguous. While there's no debate on whether it's okay to pee in the pool—the fact is, it's just plain gross—many of us choose to neglect the unwritten rules of hygiene, and heighten other people's risk of contracting unwanted germs, diseases, and illnesses.

The flipside of that, however, is that many people are unknowingly engaging in risky activities, doing seemingly normal things that are actually far nastier than they think. We compiled a list of things we thought were surprisingly disgusting, and ran them past our experts to weigh in. But honestly, just...stop.

To cut your risk of viral infections, do what your mother always told you to do and wash your hands.

Blowing the candles out on a birthday cake

Now that someone has said it, you can already envision it happening. The overjoyed young boy on his tenth birthday, wishing for a new Xbox, closes his eyes and takes a deep breath in, ready to put out the candle fire with a mixture of youthful wind power and saliva.

"Kids are virtual petri dishes of everything," says Donna Duberg, an assistant professor of clinical laboratory science from Saint Louis University.

According to a study done by Clemson University, significant increases in bacteria were found in the icing on birthday cakes after the candles were blown out. Given the fact that this tradition has been in existence for decades, it's tough to gauge the threat of these bacteria. That said, it's probably not a smart idea for a sick kid to be spitting all over cake for the entire party.

"Kids are typically more likely to have colds and flues," says Charles Gerba, a professor of microbiology and environmental sciences at the University of Arizona.

If you're paranoid and can't get the image of saliva falling like rain all over icing, take Duberg's advice and give the birthday child a smaller cake or a collection of cupcakes to blow out instead—and then have all to themselves. It'll minimize the damage, and the cake still lives on.

Feel a sneeze coming on? Try these 10 Ways to Stop a Cold in Its Tracks.

Bringing your coffee into the bathroom

You've just left the break room with a fresh cup of joe when an unexpected urge causes you to take a detour to the bathroom. What's wrong with just popping that on the sink while you take care of business?

"Let's get real, you shouldn't be taking anything in there with you," says Duberg.

The fecal matter that is crawling all over the bathroom will inevitably latch on to your cup and follow you back to the office. Be advised: the cross contamination doesn't stop at your desk.

"Office coffee cups are loaded with fecal matter," says Gerba. "Because they're cleaned with sponges, it's easy for fecal bacteria to grow in large numbers."

Think twice before you bring your beverage into the can. And while you're at it, here are 8 health flubs you didn't realize you were making.

Bobbing for apples

Your vision of this classic Halloween party game is now forever warped with the thought of blinded contestants hopelessly shoving their open mouths into an opaque pool of murky apple water. All that saliva swirling about in that pot is a recipe for disaster.

"Strep throat is transferred through saliva," says Duberg.

Any instance where your mouth is engaging with foreign saliva puts you at risk for contracting strep throat, like drinking out of the wine cup at church, Duberg explains. Additionally, Gerba suspects the exposure of one's nose, eyes, and mouth is a gateway for infection.

"I wouldn't want to get anyone in there with a cold, flu or diarrhea ahead of me," says Gerba.

So what's the solution to avoiding contamination from this classic party game?

"There are alternatives where people are using chopsticks instead of their mouths to pull them out," says Duberg.

Bob at your own risk, but it seems pretty wise to avoid shoving your head into a pool of everybody's spit.

Bugs in your food? It's legal, thanks to the FDA. Learn which gross bugs are hiding in your fruits and veggies.

Sharing your headphones

Earwax is the most obvious grossness factor when sharing headphones and earbuds, but according to Duberg it should be the least of your concerns.

"You're worried about earwax, but that doesn't grow anything. It's the ear canal that grows stuff," she says.

She's more concerned with spreading bacteria like pseudomonas aeruginosa, which give off an odor that resembles sweet grapes, or causing otitis media (ear infections), a common risk for children who contract streptococci as a result of frequent sharing of headphones and earbuds. At the end of the day, that coat of visible earwax may seem like the grossest part, but the true danger lurks deeper. Keep your headphones to yourself.

Want to keep your hearing sharp? Here's how you can dodge the most serious threats to your ears.

Bellying up to the buffet

There are plenty of good things about buffets: unlimited food, tons of variety, and, well, that's it. Unfortunately—as much as you might be comforted by that sneeze shield—buffets can be major breeding grounds for food-borne illnesses.

"The risks are much more common than people think," says Gerba.

He cites an example where a norovirus outbreak at a wedding was traced back to a metal serving spoon in the buffet line, contaminating all the guests. There have been numerous incidents where buffets have cultivated diseases—E.coli, Salmonella, and Shigella are all potential risks when standing in line. Duberg recognizes the potential threat buffets can pose, and urges caution.

"Try to use disposable utensils—one spoon for one container—and uset hand sanitizer if you've got finger foods," Duberg says.

Here are five things that you should think twice before touching.