Study Finds the 3 Dirtiest Body Parts You're Forgetting to Wash in the Shower

Yes, you need to clean inside your belly button!

It’s easy to think of bathing as almost instinctual—something we’ve always known how to do effectively. But, as we learned during the 2019 internet debate over whether it’s necessary to wash your legs in the shower, we’re not all on the same page when it comes to how to bathe ourselves properly. That said, along with constantly being told to wash your hands, you may recall a parent, grandparent, or other trusted adult reminding you to wash behind your ears, between your toes, and inside your belly button when you take a bath or shower.

Curious about whether previous generations’ advice has had an impact on our health and hygiene, researchers at George Washington University (GW) decided to put what they refer to as “The Grandmother Hypothesis” to the test. Here’s what to know about the study’s findings, as well as how to safely and effectively clean these three often-overlooked body parts in the shower, according to a dermatologist and family medicine physician.

Related: How to Take the Most Relaxing Bath, According to Science

What Is the Grandmother Hypothesis?

When Keith Crandall, PhD, professor of biostatistics and bioinformatics at GW, was a child, his grandmother directed the children in his family to “scrub behind the ears, between the toes, and in the belly button,” he explained in a university news release on the study. These instructions are the basis of what Crandall and the rest of the team of researchers at the GW Computational Biology Institute refer to as the “Grandmother Hypothesis”: that people don’t wash these three body parts as frequently as the skin on, say, their arms and legs. As a result, these areas may harbor different kinds of bacteria—including some that could negatively affect a person’s health.

The Study Findings: Does the Grandmother Hypothesis Hold Water?

After analyzing a collection of skin swabbing samples collected from 129 graduate and undergraduate students, the researchers found that microbes from areas typically washed regularly—in this case, forearms and calves—were more diverse, and, consequently, potentially part of a healthier microbiome than samples from behind the ears, between the toes, and inside the belly button.

In the study, published in September in the journal Frontiers in Microbiology, Crandall and his colleagues explain that when the moist, oily areas of the body like these aren’t washed often enough, it gives certain undesirable microbes the opportunity to shift the entire microbiome, and potentially result in skin conditions like eczema or acne. The authors also note that given the relatively small sample size, and the limited body parts swabbed for the study, more research is needed to get a more definitive picture of how washing—or not washing—various areas can impact our health.

According to Laura Purdy, MD, a Miami-based family medicine physician who was not affiliated with the GW study, this research reinforces the need to clean all the skin on our body when bathing—including the “hard-to-reach” and “easy-to-forget places” like behind our ears, between our toes, and inside our belly button.

“Washing our body gets rid of dirt, odor, and allergens that have built up on your skin throughout the day, but it also removes your body's dead skin cells, sweat, and natural oils found on your skin,” she explains. “Your skin can also be hosting some bacteria, viruses, or fungi, so washing these areas is important to cleanse your skin.”

Now, let’s take a closer look at each of these three body parts to find out what can happen when they don’t get a thorough cleaning, as well as how to clean them properly.

Related: We Asked Derms How Often You Should Shower—Here's What They Said

Behind the Ears

Anywhere that there’s a crease or fold in the skin—like behind the ears—the body oils (also known as sebum) and skin cells that your body sheds naturally, plus any surface dirt, can get trapped and irritate the skin, says Stacey Tull, MD, a double-board-certified dermatologist and micrographic dermatologic surgeon based in Cottleville, Missouri, who also was not involved with the GW study. “The buildup of skin debris can become an inflammatory skin condition known as ‘seborrheic dermatitis,’” she explains. “This is the skin counterpart to dandruff on the scalp.”

Seborrheic dermatitis can cause white or yellow flakes to form on the scalp—including behind your ears, Dr. Purdy explains, noting that these inflamed areas may start to itch and become flaky.  “Any inflammatory condition of the skin can lead to cracks in the natural skin barrier, allowing bacteria in and causing infections,” Dr. Tull adds.

Related: Dermatologists Explain What Sebaceous Filaments Are and How to Get Rid of Them

Along the same lines, if you’re not washing behind your ears regularly, Dr. Purdy says that you may notice the skin in that area becoming sensitive or irritated, or eventually, develop eczema. “If you have your ears pierced, you absolutely want to focus on washing this area to avoid infection,” she adds. 

Lastly, there’s the odor. “You have sweat glands behind your ears, so sweat is produced,” says Dr. Purdy. “Sweat, when exposed to bacteria, can start to smell over time.”

There’s no special method or product you need to wash behind your ears: the key is remembering to do it. “Washing behind the ears should be no different than washing the rest of your body,” Dr. Tull says.

“Use whatever type of soap your skin is used to. If you use a washcloth elsewhere, use it here, too. I personally just use soap and the friction of my fingers to wash my entire face and body.” Dr. Purdy agrees, saying that simply using your fingertips to rub gently behind your ears will get the job done.

Between the Toes

While most of the water and soap from your shower probably flows over your feet and toes before going down the drain, this doesn’t sufficiently clean the areas between your toes.

“Because the skin between the toes does not produce as much oil as other areas of the body, the consequences of not washing here are slightly different,” Dr. Tull says, noting that the main component of buildup is dead skin cells and dirt. It could also lead to nail fungus, she adds.

Dr. Purdy also points out that our feet tend to sweat a lot, and because wearing shoes traps that perspiration in place, it can result in the growth of bacteria and fungus. “You could develop athlete's foot, which is a fungal infection of skin that typically occurs in between the toes,” she says. “Your feet may be itchy, peeling, scaly, and your skin may develop a rash or crack.”

Not washing between the toes regularly can also result in bacterial dermatitis or cellulitis, a bacterial skin infection that can spread up the leg, Dr. Tull says. “It is especially important for diabetics to wash their feet and between their toes [as they] have a much lower threshold to contract skin infections,” she notes.

Washing between your toes is also pretty straightforward. According to Dr. Tull, it should be done whenever you shower: ideally, every one or two days. Anyone who isn’t able to take a full shower or ball that often can clean between their toes in a foot bath. “Again, using what you would normally use to wash your body should be fine for the feet,” she adds.

Similarly, Dr. Purdy recommends using soap to wash your feet, including between your toes, and then thoroughly rinsing them. “Also, remember to change your socks,” she says. “Socks have a lot of buildup and bacteria that accumulate, so it's important to wash them between wears.”

Inside the Belly Button

Whether you call it your “belly button” or “navel,” you shouldn’t forget to wash it regularly, both doctors urge. In addition to being dark and moist, the belly button also has multiple skin folds, creating the ideal environment for the accumulation of dead skin cells, sweat, and other microorganisms, like bacteria and fungi, Dr. Purdy says.

Not only could this result in an odor, but the skin-on-skin rubbing can make the area prone to infections—the most common being staph and yeast infections, she explains. “This area can become extremely irritated, infected, inflamed, red, itch, become raw, and even scab or develop a yellow crust,” Dr. Purdy notes.

Cleaning your belly button every day or two should be sufficient, Dr. Tull says, adding that like the parts discussed above, no special soap is needed. If you have sensitive skin or conditions like eczema, Dr. Purdy recommends choosing a soap or body wash for your particular skin type, and says that those with a navel piercing “absolutely want to take care of the area and wash regularly.”

All you need to do to clean your belly button is use a soapy finger to gently rub the inside, then rinse. Some people prefer using a cotton swab, but Dr. Tull stresses the importance of using this, or any tool, with a light touch. “Care should be taken to not be too aggressive, such as digging into the area with a Q-tip, because this can induce extra trauma,” she says.

Related: How to Get a Healthy Scalp, According to Experts

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