Here's What That Gunk Underneath Your Fingernails Is Really Made Of

Plus, tips for getting rid of the nasty stuff for good (Photo: Shutterstock)

Doesn’t it always seem like no matter how much you scrub your hands, the dirt underneath your fingernails never completely disappears? It’s seriously frustrating. If you’ve ever wondered why grime keeps accumulating there—and what that beneath-the-nail stuff is really made of—here’s your answer.

It turns out that the gray gunk is not only pretty common, but pretty harmless, too. “The ‘gunk’ underneath fingernails is most commonly the keratin debris from the underside of the nail, as well as skin cells from the nail bed,” says Dana Stern, M.D., a dermatologist with practices in New York City and Southamptom, New York (she’s actually one of the few doctors in the country who specializes in nail health). What else can be living under there? Dirt, lint, and personal care products are also common culprits.

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Meanwhile, if the gunk turns from gray to green, that means you’ve got bacteria underneath your nails. “Certain bacterial organisms have a particular affinity to the nail and surrounding nail folds,” says Stern. “Pseudomonas, for example, is commonly found on nails and produces a green pigment that nail technicians often refer to as 'the greenies.’” (See the image below for what this looks like, from a 2014 study published in the journal Annals of Dermatology.)

Annals of Dermatology

This bacteria can cause an infection (yikes!), but it most often occurs with women who wear artificial nails. Not only do artificial nails carry a higher risk for trapping pseudomonas because the nails are long, but “they can also have openings that can be perfect havens for bacteria,” says Stern.

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Your first line of defense against the icky stuff that gets stuck under your nails: Keep them short. Next, be strategic with how you wash your hands. “Digging your nails into a bar of white soap in the shower will help to pull out dirt and debris and makes the whites of your nails whiter,” says Stern. What type of moisturizer you use will make a difference, too. Thick creams, which can be goopy, tend to trap dirt, says Stern, so consider using a moisturizing oil instead.

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And skip using a nail brush. “Because they can’t be sterilized, they have the potential to continuously harbor bacteria,” says Stern. Ew. If you want to clean under your nails, use an orange stick to sweep beneath them. Just make sure to do so gently. “Overly vigorous cleaning can cause the nail to separate from the underlying nail bed,” says Stern.

More from Women’s Health:

11 Nail Symptoms You Shouldn’t Ignore  

8 Secrets from a Manicurist for Amazing Nails  

13 Nail Polish Problems and How to Fix Them    

By Shannon Farrell