What's Really Under Your Dirty Fingernails

Nobody enjoys looking down and seeing gunk in their fingernails. It is gross, yes, but have you ever stopped to wonder what it actually is?

It turns out that some degree of gray gunk is normal and harmless. According to dermatologist Dana Stern, this gunk typically consists of skin cells from the nail bed, as well as keratin debris from beneath the nail (via Women's Health). Keratin is the key protein that makes up your nails, as well as your skin and hair (per Healthline).

According to Women's Health Magazine, other causes of fingernail gunk could include lint, dirt, and personal care products. If the gunk is green, then you may have a case of "green nail syndrome" (chromonychia) that is likely caused by Pseudomonas aeruginosa (per Annals of Dermatology). This may happen more often to people with artificial nails, because the nails are long and have openings, making them more likely to trap bacteria. Other culprits of green nail syndrome include trauma (such as nail-biting) or the nails being submerged in water too frequently (per Dermatology Advisor).

A 1988 study discovered that most participants had hundreds of thousands of bacteria under each fingernail (via Journal of Clinical Microbiology). This is far greater than the hundreds of bacteria found on the hands in general. The Centers for Disease Control and Prevention (CDC) notes that fingernails can contribute to the spread of some infections such as pinworms.

The CDC advises against biting your nails, and recommends keeping your nails short and regularly cleaning underneath your nails with soap and water. According to Stern, you may want to wash your hands strategically. Stern tells Women's Health that digging your nails into a white bar of soap can help whiten your nails by getting rid of dirt. She also suggests opting for moisturizing oil, as opposed to thick creams, the latter of which can trap dirt.

In addition, Stern recommends using an orange stick to gently sweep under your nails. Of course, you should clean any nail grooming tools before you use them, according to the CDC.