Those thousands of genes we tote in our genomes poke their noses into everything from our hair color to our risk for heart disease--they even have something to say about whether we'll let fungi feed and thrive under our toenails.
The critters causing toenail fungus aren't rare. They're the same little brutes that cause athlete's foot, and damp showers can be positively swimming with them. Yet the fungi in question--from a group called "dermatophytes," or "skin plants"--invade some people's toes and not others'. A study of French families with toenail fungus revealed that when one spouse had the fungus, the other spouse didn't catch it after 18 to 60 years of living, showering and sleeping together.
"If you're a person who's not going to get it, you're not going to get it--you could walk through a field of it," says Dr. Monica Lawry, a Sacramento nail specialist.
Yet in the French study, about half of these people's kids went on to get infections--rather as if susceptibility to the condition was being handed down as a one-gene, dominant trait. It is unlikely that there will be a rush to confirm this one-gene business and track down the DNA involved. Toenail fungus, after all, is hardly life-threatening.
"It feeds on the skin; it doesn't go into the bloodstream, doesn't spread to other parts of the body," says Dr. Richard Scher, nail specialist and professor of dermatology at Columbia University. "It does not attack the liver, for example, or the brain."
Yet for the estimated 2% to 18% of the population afflicted with it, there's no doubt it can be distressing--causing yellowing, thickness and flakiness of the nail area and making the nails lift away from the nail bed. Plus, having the fungus can hurt a lot if someone stomps on an infected toe.
And, once there, it's not like a wart that might one day decide to disappear. Toenail fungus stays put for good unless stern steps are taken to eradicate it.
Happily, genes aren't the whole story--giving the potential host a modicum of control.
The fungus needs opportunity. Trauma to the nail allows the fungus to gain entry, which is why athletes--who spend a lot of time leaping about bashing their nails against the ends of their shoes--are more likely to end up with infections. (Be nice to your nails.)
And, of course, to get the fungus, you have to be exposed to it. Toenail fungi like damp, moist places such as swimming pools and health club showers and the deep, dank depths of sweaty sneakers. (Avoid walking barefoot in such places, control perspiration, and toss out ancient, infested footwear.)
What's more, if the fungi are permitted to take up residence in patches of athlete's foot, they will make their move when nail trauma strikes and send their long, spaghetti-like filaments into the toenail area. (Treat your athlete's foot.)
The likes and dislike of the fungus explain what has often mystified us--why one hears lots about toenail fungus but precious little about fingernail fungus. Fingernails get less of both trauma and dampness. Still, people who are really prone to the fungus and traumatize their fingers (during basketball or tennis, for instance) can get the finger variety too.
During a nail infection, the fungus burrows deep, invading both the nail bed and nail matrix (the tissue that makes the nail). Thus, while topical drugs will help in light cases, a well-developed infection won't respond. (Nor, says Scher, will it react much to dousing the nail in Clorox or vinegar.) You have to swallow anti-fungal drugs so they can make their way through the bloodstream to those tissues.
It can take four months to a year to grow the toenails back--and (here's the kicker) once you stop taking the medications, the growth can come back again if you're not squeaky-clean careful about avoiding exposure to the fungus.
Since other things can cause nails to alter their appearance, Scher and Lawry emphasize that it's important to get samples analyzed for actual presence of the fungus. Lawry once had a patient come to her with a "fingernail fungus" problem for which he'd been treated for some time: "It was totally the wrong diagnosis, and there was no way it'd ever respond to anti-fungals," she says.
Stained with dyes, safely under the microscope, the fungus appears as long, colored strands--almost festive-looking. It's hard to imagine it could make such a mess of a nail.
But then, Ebola's pretty cute-looking too.
If you have an idea for a Booster Shots topic, write or e-mail Rosie Mestel at the Los Angeles Times, 202 W. 1st. St., Los Angeles, CA 90012, firstname.lastname@example.org.