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Hand sweet home

Working to understand—and protect—the hand microbiome

For many of us, the pandemic has inspired a new obsession with keeping our hands clean. Yet much is still unknown about the microbes that live on our hands and how to protect their health—and ours. Skin microbiome researcher Kelly N. Haas of the UMass Amherst biology department recently began a research partnership with GOJO Industries—the makers of Purell—to study the relationship between the microbiome, hand hygiene, and hand health.

Illustration of microbes. Text reads, “Microorganisms help skin defend against ‘bad’ bacteria.”

Research into the skin microbiome is barely a decade old, and scientists are still in the process of answering fundamental questions about what makes up the hand microbiome. They believe it is composed of millions or even billions of microorganisms—primarily bacteria and yeasts/fungi, but possibly also viruses, bacteriophages, and microscopic eukaryotes. These microorganisms provide important protection for humans’ first line of defense—the skin—by shielding us from “bad” bacteria.

Illustration of microbes. Text reads, “Bacteria, yeasts, fungi, and viruses can be found on palms.”

According to Haas, a healthy skin microbiome provides a low pH—which, combined with the physical competition for space and nutrients, prevents colonization and proliferation by most pathogens. The microbiome also trains and regulates the immune system so that the body can adjust the skin microbiome to limit certain pathogens. “This self-regulation has its limits,” says Haas, “which is why we rely on targeted hand hygiene to keep ourselves healthy and reduce disease transmission.”

Illustration of microbes and germs. Text reads, “One’s hand microbiome is a reflection of their environment”

In addition to getting a clearer picture of what a healthy hand microbiome looks like, Haas is also seeking to understand what changes when that microbiome is disrupted—for example, by handwashing or sanitizing. The goal is to learn how to manipulate that process for our benefit.

But the hand microbiome is complicated to assess because people are constantly touching things. The trick is teasing apart which microbes belong there versus which ones were picked up from the environment.

“For example, we know that farmers who work in the dirt end up looking like they have a soil microbiome on their hands,” Haas explains.

Illustration of microbes. Text reads, “Billions of microorganisms can live on a single hand.”

Haas is also beginning work to close a major gap in scientists’ knowledge. Over half of the organisms processed in her lab’s sequencing surveys cannot be mapped to known species. Her new research will develop a collection of hand isolates (pure cultures of individual organisms isolated from human hand microbial communities) and their genome sequences—an enormous boon for hand microbiome research.

The Risks of Overcleaning

“Because of the pandemic, many people have gone overboard about cleaning everything,” says Haas. The visible signs of over-washed hands, familiar to many of us, include a dry, red, itchy rash called atopic dermatitis.

Illustration of microbes. Text reads, “Over-washing and over-sanitizing can damage microbes.”

But this discomfort may also signal damage at a microbial level. Haas describes a trade-off between hygiene and health, saying it’s both futile and potentially dangerous to try to kill all microbes in the environment. “When we try to kill everything off, we end up making it easier for certain organisms to colonize those spaces because there’s not that normal colonization resistance anymore,” she says. “People who are really heavily washing their hands or overusing hand sanitizer run the risk of harming their hand health by disrupting that microbial and lipid barrier.”

Imagining Better Products

Products currently available to cleanse hands include soap—which washes off microbes but doesn’t usually kill them, and sanitizers—which typically use ethanol, a broad-spectrum killing agent. Scientists like Haas hope to translate their research into developing more microbiome-friendly products in the next three to five years, exploring the possible use of probiotics, prebiotics, and postbiotics to support the microbes that should be living on hands.

It’s both futile and potentially dangerous to try to kill all microbes in the environment.

While each of these options has its own pros and cons, they all have the potential to “give a competitive advantage to the organisms we want to be growing on hands and help them repopulate themselves faster after a hand hygiene event,” says Haas.

Advice for Healthy Hands

Illustration of microbes. Text reads, “Killing certain organisms with soaps can help others flourish.”

To keep her hands clean, Haas typically uses soap and water when she’s home, and hand sanitizer out in public. She prefers sanitizers made with ethyl alcohol, explaining that it can actually be gentler on hands than soap and water, which breaks up the lipid barrier and pulls water out and down the drain. Antibacterial soaps are not necessary unless a person has had known contact with a “large quantity of infectious bacteria,” she says. In general, Haas advises people to clean their hands after coming into contact with high-touch surfaces or those in restrooms. And always wash before eating or after blowing your nose.