What really lives under the nails we chew?

Our fingernails can be a bit of a guide to what we're like as people — colourful, traditional, or when they're chewed down, stressed out. You may prefer the natural look but in a nail bar you can let your imagination run wild, from long acrylic talons to custom paint jobs that are works of art.

But have you ever wondered what nasty bacteria hide beneath your nails? Prepare to be shocked as our reporter Leila McKinnon investigates.

The test

Fingernails are actually dead cells made of the same stuff as our hair, a protein called keratin. We could probably get along fine without them, but they help us do fiddly things, like text messaging and scratching ourselves.

But, did you know when you scratch yourself with your nails you can actually cause infections?

Dr David Katz of Yale University in the United States knows all about the dangers.

"Let's just say you had an itch and you scratched a little bit too hard and you abraded your skin, germs living under your fingernail would get under your skin barrier and cause infection to yourself and, obviously, we have the same potential to transmit germs to other people," he says.

This definitely needs some further investigation so we've asked some friends along to help out.

  • Barbara has long acrylic nails.
  • Patti favours the long unpainted nail.
  • Michelle has short painted nails.
  • Yuka has short unpainted nails.

Although Leila's a bit nervous about what might be lurking under her nails, she too is putting her short, painted nails to the test.

Leila: So what's the procedure here?
Dr Katz: We're going to culture your fingernails.
This entails taking a swab from under a fingernail and letting the bacteria grow. Then, after a wash of their hands, Dr Katz takes another swab.

What we're left with is five different samples which are then placed into the incubator to grow those bugs.

Dr Katz: In three days time they will have grown out on these plates and again there will be a characteristic appearance that will tell us exactly what they are.


Which nail had the least number of bacteria? The winner is Natalie who wears short, painted nails.

Why did Natalie's nails win? Because they're easier to keep clean.

"This person also did a good job washing their hands," says Dr Katz.

What about the worst? The big loser is the long, unpainted nails owned by Patti.

"The sort of bluish grey [bacteria] are probably staphylococcus and those with a greenish tint are normal mix skin flora if we look [at the washed hands sample] there's a bit less growth," says Dr Katz about Patti's samples.

Staphylococcus can cause anything from impetigo to toxic shock and even skin eating disease and this strain of staph can easily infect newborns and the elderly.

The other nails had varying amounts of bacteria. Whether or not they were painted didn't seem to matter in our test — how you washed them did.

So what about Leila's nails?

Dr Katz: Let's see how your hand washing did.
Leila: Looks like I got them dirtier!
Dr Katz: It certainly didn't make a great deal of difference — you could mix these up and I'm not sure you'd be able to say what's what.
Leila: You'll have to show me how to wash my hands properly!

Not only having the right fingernails is important, but also the right hand-washing technique to keep those nails clean.

Queenslander Rachelle Williams is a food safety and hygiene consultant who works with food businesses to make sure they meet the food standards code.

"When you're washing your hands you need to make sure you're getting under the fingernails and particularly the tips. If someone has long fingernails they must keep them clean. The Food Standards Code does require certain things with fingernails and they include: you're not allowed to have attachments, so you're not allowed to have those acrylic sort of nails; you're not allowed to wear fingernail polish, again it can be a contamination source; and I know that there's fingernails out there that you can put studs on — they would be a definite no. So if you're going to have long finger nails, keep them clean and scrub them down. But besides that I would recommend in food businesses and at home not having long fingernails," she says.

There you have it — long fingernails are the enemy, but if you must have them, Rachelle recommends the "twenty-20 rule". That's: wash your hands with soap for a count of twenty and then rinse them for a count of twenty. For the cleanest results, use antibacterial soap and dry with a paper towel.

Of course, there are other ways that nasty bacteria from under your nails can end up in your mouth — nail biting. It's a hard habit to break and sometimes it's not just your hands that suffer.

Dr Stephen Chu is Clinical Associate Professor at the New York University College of Dentistry and, believe it or not, a lot of his patients are nail biters.

Leila: Can biting your nails damage your teeth?
Dr Chu: Yes it can.
Leila: What does it do?
Dr Chu: It actually puts extra stress on the teeth, that's not usually there from normal eating and things like that. So when patients actually bite with their nail they rip with it and it puts a lot of stress and tension on their teeth. And if the teeth are weak to begin with, it can actually chip them.

Dr Chu insisted on seeing Leila's teeth.

Dr Chu: Do you bite your nails? Or are there other foreign objects that you put in your mouth, like bobby pins or things like that?
Leila: I know that one time part of a set fell on my head and I chipped my front tooth.
Dr Chu: So the teeth actually had a traumatic injury where they hit each other very quickly and they caused some breakage.

The good news is Dr Chu gave Leila's teeth the all clear. But he warned that nail biting can do just as much damage as not cleaning your teeth.

So think about that, unless you really like going to the dentist!

Fast facts

  • We all have to trim our fingernails, but do they keep growing at a constant rate? No, they don't. Fingernails grow faster on pregnant women, they also grow quicker when you're younger, grow faster on your more active hand and they grow more in summer than winter.

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