By Jason G Goldman

Washing your hands is the first defence against all kinds of nasty bacteria. But do you wash under your fingernails? Maybe you should…

You probably know that handwashing is among the best means of preventing the spread of germs. In many places, public health laws are in place to ensure that those in the food service industry keep their hands clean. On the other hand, no amount of scrubbing can ever rid the hand of all its bacteria.

The impossibility of sterilisation is why doctors and nurses so often wear gloves while interacting with patients. Indeed, nearly a hundred years ago, physicians began to realise that bacteria would always show up in tests even after multiple re-washings. But it wasn’t until the early 1970s that researchers began to identify the reason that hand-dwelling bacteria was so persistent.

It turned out that covering the fingertips could keep hands cleaner longer. Though it’s not the fingertips which are so full of bacteria, but the fingernails. These thin keratin shields, made of the same stuff as rhino or impala horns, harbour a bacterial menagerie.

It wasn’t until the late 1980s that scientists began to poke around under our fingernails to see who, exactly, lives there. In one 1988 study, a trio of researchers from the University of Pennsylvania’s Department of Dermatology swabbed the hands of 26 adult volunteers, all employees of the university’s medical school who did not interact with patients.

They found that the space under the fingernails, also called the subungual region, was “an important site” for harbouring bacteria. Other parts of the volunteers’ hands were home to hundreds to thousands of bacteria, while the subungual areas yielded hundreds of thousands of bacteria per fingertip. The fingernails harboured the same types of bacteria as the rest of the hand, just a lot more of them.

The researchers reasoned that could be because the space between the skin and nail creates a perfect environment for the growth and proliferation of these minute lifeforms, thanks to both the physical protection provided by the nail and all that moisture. The prior findings that persistent scrubbing doesn’t sterilise the hand, combined with the finding from their study “that there are significant numbers of bacteria in the subungual compartment suggest[s] that this hand region may be relatively inaccessible to antimicrobial agents during normal hand-washing procedures,” they wrote.

Think about it: the space under your fingernails is completely impervious to the best, and simplest, means we have of preventing the spread of diseases.

Indeed, a small but thriving area of research continues to probe the very nature of the microbial life living on the fingernails of nurses. And not just natural nails, but also artificial ones, or ones covered in polish.

In 1989, just one year following the University of Pennsylvania study, a group of nurses wrote, “although unanswered questions concerning the safety and practicality of artificial nails remain, many health care workers have succumbed to fashion trends and are now wearing artificial nails”.

The researchers wanted to see whether 56 nurses with artificial nails, which tend to be longer than natural nails and are almost always covered in nail polish, had more bacteria on their fingertips than 56 nurses with natural nails. They also wanted to see whether handwashing was more or less effective for those with artificial nails.

They discovered that nurses with artificial nails had more bacteria on their fingertips than did those with natural nails, both before and after handwashing. That’s not to say that they were actually transferring more bacteria to their patients, necessarily, only that the bacteria living on their fingertips were more numerous. Still, the assumption is that more bacteria at least increases the potential for pathogen transmission.

Similar studies published in 2000and 2002 yielded similar results. But by then, nursing researchers had evidence that artificial nails were also associated with poor handwashing practices, which only served to compound the problem. And artificial nails, they realized, were also more likely to tear disposable gloves.

Painted, natural nails, on the other hand, tell a different story. The fear with polish is that tiny chips or cracks in the paint could harbour bacteria. In 1993, nurses from Johns Hopkins Hospital in Baltimore looked at the fingernails of 26 adult women who were employed by the hospital, but not involved in patient care. All had short fingernails, and all were assessed both before and four days after nail polish was applied.

Nail polish on natural nails did not seem to affect the richness of fingertip bacterial micro-biodiversity in the same way as polish on artificial ones, however. “Keeping nails short and clean, therefore, is probably more important than whether or not nail polish is worn,” the researchers concluded. Another study conducted the following year reached a similar conclusion. While polished nails more than four days old had more bacteria, freshly polished nails were perfectly safe.

Some two to three million people die each year from diarrhoea; it’s thought that handwashing with soap could save perhaps a million of them. And it probably can. But in addition to handwashing, the best course of action seems clear: pay special attention to the subungual compartment beneath your fingernails when washing your hands, and for the least bacterially hospitable fingertips, keep them short and clean.

All of which should give you pause before biting your nails.

/By BBC/