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The Bugs on Us

Meet some of the tiny residents that call our bodies home

January 17, 2022
By Jennifer Barone

AS YOU READ, THINK ABOUT the diversity of life that lives in and on the human body.

POWER AND SYRED/SCIENCE SOURCE

IN THE FAMILY: People pass on Demodex mites to their children, so scientists can trace a person’s ancestry based on genetic analysis of their mites.

Don't panic! Right now, there are thousands of tiny mites on your face. These eight-legged creatures live inside your hair follicles—pouches in the skin from which hairs grow. You shouldn’t bother rushing to the sink to scrub them off though (it wouldn’t work anyhow). Having face mites is totally normal, says biologist Megan Thoemmes of the University of California, San Diego.

Right now, thousands of tiny mites are on your face. These eight-legged creatures live inside your hair follicles. Hairs grow from these pouches in the skin. But you shouldn’t rush to the sink to scrub the mites off. (It wouldn’t work anyhow.) Having face mites is totally normal, says Megan Thoemmes. She’s a biologist at the University of California, San Diego.

Thoemmes worked on a project that examined the faces of more than 4,000 people for these critters, called Demodex mites. “We haven’t found a single person without them,” she says. Demodex can live all over our bodies. But they’re most abundant on our faces, where they may eat dead cells and an oily substance called sebum. The mites are probably harmless and may even benefit us in some unknown way. “They’re just hanging out, like thousands of little friends who are always with you,” says Thoemmes.

Mites are just one of the many microscopic organisms that live on us. “The body is its own ecosystem that hosts thousands of species,” says Thoemmes. “It’s like a forest, with mites, fungi, and bacteria interacting and working together to form a community.” Many of our body’s regular residents, like the microbes in our gut that help with digestion, play important roles in keeping us healthy. But our bodies sometimes pick up problematic invaders too. Unwanted parasites like head lice can drink blood from our scalps, while certain worms can infest our intestines, robbing us of nutrients. Yikes!

Thoemmes worked on a project that looked for these critters, called Demodex mites. The project examined the faces of more than 4,000 people. “We haven’t found a single person without them,” she says. Demodex can live all over our bodies. But they’re most common on our faces. There, they may eat dead cells and an oily substance called sebum. The mites are probably harmless. They may even benefit us in some unknown way. “They’re just hanging out, like thousands of little friends who are always with you,” says Thoemmes.

Many microscopic organisms live on us. Mites are just one of them. “The body is its own ecosystem that hosts thousands of species,” says Thoemmes. “It’s like a forest, with mites, fungi, and bacteria interacting and working together to form a community.” Many of our body’s regular residents are important for keeping us healthy. For example, the microbes in our gut help with digestion. But sometimes, our bodies pick up troublesome invaders too. Unwanted parasites like head lice can drink blood from our scalps. And certain worms can infest our intestines and rob us of nutrients. Yikes! 

SKIN DWELLERS

Our skin is home to a multitude of microbes, including bacteria, fungi, and viruses. Different parts of our skin host unique combinations of these inhabitants.

Our skin is home to a multitude of microbes, including bacteria, fungi, and viruses. Different parts of our skin host unique combinations of these inhabitants.

ILLUSTRATION: HARVEY SYMONS; DATA SOURCE: OH ET AL., NATURE, 01 OCTOBER 2014

DIG INTO THE DATA: Which body part shown above hosts the largest percentage of bacteria? Which has the largest percentage of viruses?

DIG INTO THE DATA: Which body part shown above hosts the largest percentage of bacteria? Which has the largest percentage of viruses?

SKIN DWELLERS

Our skin is home to a multitude of microbes, including bacteria, fungi, and viruses. Different parts of our skin host unique combinations of these inhabitants.

Our skin is home to a multitude of microbes, including bacteria, fungi, and viruses. Different parts of our skin host unique combinations of these inhabitants.

ILLUSTRATION: HARVEY SYMONS; DATA SOURCE: OH ET AL., NATURE, 01 OCTOBER 2014

DIG INTO THE DATA: Which body part shown above hosts the largest percentage of bacteria? Which has the largest percentage of viruses?

DIG INTO THE DATA: Which body part shown above hosts the largest percentage of bacteria? Which has the largest percentage of viruses?

Outnumbered

Your body contains more microbes than human cells. Many reside in the gut and are expelled in poop, which may temporarily tip the balance in favor of human cells.

Your body contains more microbes than human cells. Many reside in the gut and are expelled in poop, which may temporarily tip the balance in favor of human cells.

SOURCE: SENDER ET AL., PLOS BIOLOGY, 19 AUGUST 2016

DIG INTO THE DATA: Based on the diagram, roughly what percentage of cells in the human body are microbial?

DIG INTO THE DATA: Based on the diagram, roughly what percentage of cells in the human body are microbial?

Outnumbered

Your body contains more microbes than human cells. Many reside in the gut and are expelled in poop, which may temporarily tip the balance in favor of human cells.

Your body contains more microbes than human cells. Many reside in the gut and are expelled in poop, which may temporarily tip the balance in favor of human cells.

SOURCE: SENDER ET AL., PLOS BIOLOGY, 19 AUGUST 2016

DIG INTO THE DATA: Based on the diagram, roughly what percentage of cells in the human body are microbial?

DIG INTO THE DATA: Based on the diagram, roughly what percentage of cells in the human body are microbial?

GUT CHECK

IMAGE: MYBOX/SHUTTERSTOCK.COM

Bacteria in our digestive system play many beneficial roles in our body. The right mix of gut microbes is important for several aspects of our health.

Bacteria in our digestive system play many beneficial roles in our body. The right mix of gut microbes is important for several aspects of our health.


LINE OF DEFENSE:

Microbes lining the digestive tract create a physical barrier against invading pathogens that could cause illness.


LINE OF DEFENSE:

Microbes lining the digestive tract create a physical barrier against invading pathogens that could cause illness.


NUTRITION:

Gut bacteria help absorb minerals, like calcium and iron, and make vitamins, like B and K.


NUTRITION:

Gut bacteria help absorb minerals, like calcium and iron, and make vitamins, like B and K.


ENERGY:

Intestinal microbes help our bodies break down starch in foods that we normally couldn’t digest, allowing us to draw more energy from the foods we eat.


ENERGY:

Intestinal microbes help our bodies break down starch in foods that we normally couldn’t digest, allowing us to draw more energy from the foods we eat.


BRAIN CONNECTION:

Research suggests that gut bacteria produce chemicals that influence our mood.


BRAIN CONNECTION:

Research suggests that gut bacteria produce chemicals that influence our mood.

DIG INTO THE DATA: Certain medications to treat infections can kill gut bacteria. How might that affect a person’s health? Give two examples.

DIG INTO THE DATA: Certain medications to treat infections can kill gut bacteria. How might that affect a person’s health? Give two examples.

GUT CHECK

IMAGE: MYBOX/SHUTTERSTOCK.COM

Bacteria in our digestive system play many beneficial roles in our body. The right mix of gut microbes is important for several aspects of our health.

Bacteria in our digestive system play many beneficial roles in our body. The right mix of gut microbes is important for several aspects of our health.


LINE OF DEFENSE:

Microbes lining the digestive tract create a physical barrier against invading pathogens that could cause illness.


LINE OF DEFENSE:

Microbes lining the digestive tract create a physical barrier against invading pathogens that could cause illness.


NUTRITION:

Gut bacteria help absorb minerals, like calcium and iron, and make vitamins, like B and K.


NUTRITION:

Gut bacteria help absorb minerals, like calcium and iron, and make vitamins, like B and K.


ENERGY:

Intestinal microbes help our bodies break down starch in foods that we normally couldn’t digest, allowing us to draw more energy from the foods we eat.


ENERGY:

Intestinal microbes help our bodies break down starch in foods that we normally couldn’t digest, allowing us to draw more energy from the foods we eat.


BRAIN CONNECTION:

Research suggests that gut bacteria produce chemicals that influence our mood.


BRAIN CONNECTION:

Research suggests that gut bacteria produce chemicals that influence our mood.

DIG INTO THE DATA: Certain medications to treat infections can kill gut bacteria. How might that affect a person’s health? Give two examples.

DIG INTO THE DATA: Certain medications to treat infections can kill gut bacteria. How might that affect a person’s health? Give two examples.

UNWANTED VISITORS

CNRI/SCIENCE SOURCE


HEAD LICE: These bloodsucking insects infest the scalp, causing itching and irritation for millions of Americans—primarily kids 11 and under—every year.


HEAD LICE: These bloodsucking insects infest the scalp, causing itching and irritation for millions of Americans—primarily kids 11 and under—every year.

THIERRY BERROD, MONA LISA PRODUCTION/SCIENCE SOURCE


ITCH MITES: These arthropods burrow into the skin using their mouth and front legs, resulting in an itchy condition known as scabies.


ITCH MITES: These arthropods burrow into the skin using their mouth and front legs, resulting in an itchy condition known as scabies.

STEVE GSCHMEISSNER/SCIENCE SOURCE


TAPEWORMS: These ribbon-like worms enter the body through contaminated food or water and attach to the intestines. They can grow up to 80 feet long.


TAPEWORMS: These ribbon-like worms enter the body through contaminated food or water and attach to the intestines. They can grow up to 80 feet long.

DAVID SCHARF/SCIENCE SOURCE


HOOKWORMS: These parasites enter the skin and migrate to the digestive system, where they feed on blood and cause anemia, a shortage of red blood cells.


HOOKWORMS: These parasites enter the skin and migrate to the digestive system, where they feed on blood and cause anemia, a shortage of red blood cells.

DIG INTO THE DATA: About how many stories tall would the longest-known tapeworm stretch? (Hint: One story equals 10 feet.)

DIG INTO THE DATA: About how many stories tall would the longest-known tapeworm stretch? (Hint: One story equals 10 feet.)

UNWANTED VISITORS


HEAD LICE: These bloodsucking insects infest the scalp, causing itching and irritation for millions of Americans—primarily kids 11 and under—every year.


HEAD LICE: These bloodsucking insects infest the scalp, causing itching and irritation for millions of Americans—primarily kids 11 and under—every year.


ITCH MITES: These arthropods burrow into the skin using their mouth and front legs, resulting in an itchy condition known as scabies.


ITCH MITES: These arthropods burrow into the skin using their mouth and front legs, resulting in an itchy condition known as scabies.


TAPEWORMS: These ribbon-like worms enter the body through contaminated food or water and attach to the intestines. They can grow up to 80 feet long.


TAPEWORMS: These ribbon-like worms enter the body through contaminated food or water and attach to the intestines. They can grow up to 80 feet long.


HOOKWORMS: These parasites enter the skin and migrate to the digestive system, where they feed on blood and cause anemia, a shortage of red blood cells.


HOOKWORMS: These parasites enter the skin and migrate to the digestive system, where they feed on blood and cause anemia, a shortage of red blood cells.

DIG INTO THE DATA: About how many stories tall would the longest-known tapeworm stretch? (Hint: One story equals 10 feet.)

DIG INTO THE DATA: About how many stories tall would the longest-known tapeworm stretch? (Hint: One story equals 10 feet.)

Use a magnifying glass to examine your skin on your arm. Can you identify hair follicles or pores? Draw a picture of what you see. Label where you think Demodex mites live on your skin.

Use a magnifying glass to examine your skin on your arm. Can you identify hair follicles or pores? Draw a picture of what you see. Label where you think Demodex mites live on your skin.

Use a magnifying glass to examine your skin on your arm. Can you identify hair follicles or pores? Draw a picture of what you see. Label where you think Demodex mites live on your skin.

Use a magnifying glass to examine your skin on your arm. Can you identify hair follicles or pores? Draw a picture of what you see. Label where you think Demodex mites live on your skin.

Biology
Human Body
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