“Don’t track mud in the house!”

“Wash your hands before dinner!”

“You can’t play with that. You don’t know where it’s been!”

Parents wear these phrases out like old blue jeans put through the spin cycle too many times. Many have come to see D-I-R-T as a four-letter word. Not long ago, kids made forts with sticks and mud, waded up to their knees in streams. How many do that now? Fears about dangers lurking in the muck (microbes, parasites and amoebas, oh my!) and a societal slant in favor of over-sanitization have been keeping families from letting kids do what comes naturally, which is to go outside and get a little messy.

But here’s a dirty little secret: Dirt and germs can actually be good for kids. The things small children want to do outside, like building mud castles, splashing around in puddles, and rolling down hills until their clothes are covered in grass stains may, in fact, be a grubby prescription for health and happiness.

Unfortunately, boys and girls today spend the better part of their time—up to seven hours per day—indoors in the sterile company of technology, rather than following their in-born impulses to explore the natural world with their senses. This indoor childhood is damaging to kids. In fact, in the last twenty years as kids spent less and less time outside, childhood obesity rates more than doubled, the United States became the largest consumer of ADHD medications in the world, vitamin D deficiency among children has soared, and the use of antidepressants in pediatric patients rose sharply.

When kids do leave the house, a growing body of research suggests the exact things we do in the name of protecting them from dirt and germs—such as not letting them get too messy and frequently using hand sanitizers and antibacterial products—can inhibit their mental and physical health and resilience.

Keep reading to learn how how getting down and dirty in the great outdoors can help children lead healthier, happier lives.

For the Health of It

Children who don’t spend time outside run the risk of serious health issues, such as obesity, myopia, and vitamin D deficiency, according to research. The good news is that outdoor activities kids love—like running, jumping, climbing, playing with friends, and taking nature walks—are a great strategy for keeping children healthy.

In addition, experts say, if we dig a little deeper—literally—there are even more benefits to be found. Playing in the dirt and even ingesting a little along the way, some researchers say, helps children build stronger immune systems. The Hygiene Hypothesis, first put forth in the 1980s, holds that when children are too clean and experience limited exposure to parasites, bacteria, and viruses early in life, they face a greater chance of having allergies, asthma, and other autoimmune diseases such as multiple sclerosis and type-one diabetes during adulthood.

While no one disputes the wisdom of basic, common-sense sanitation measures, such as washing hands and using hand sanitizer when soap and water aren’t available, experts say some exposure to dirt and germs does not hurt children and may very well help.

According to Dr. Joel Weinstock, director of gastroenterology and hepatology at Tufts Medical Center in Boston, “Children raised in an ultraclean environment are not being exposed to organisms that help them develop appropriate immune regulatory circuits.”

Dr. Mary Ruebush, immunologist and author of “Why Dirt is Good: 5 Ways to Make Germs Your Friends,” counts letting kids play in the dirt as immune-system-building step number one. “Let your child be a child,” she says. “Dirt is good. If your child isn’t coming in dirty every day, they’re not doing their job. They’re not building their immunological army. It’s terribly important.”

You know the smile on your child’s face when he’s covered in mud? Doesn’t it just warm your heart? Well, it is benefiting his. Dirt, says a Northwestern University study, is good for children’s cardiovascular health. Analyzing data collected from thousands of children over two decades, researchers have concluded that when children are exposed to germs and pathogens during infancy their risk of cardiovascular inflammation in adulthood, a precursor to heart attacks and strokes, is reduced. The study found that children who had early exposure to animal feces and infectious microbes like those found outside in soil resulted in lower levels of CRP, or C-Reactive Protein, a biomarker for cardiovascular problems later in life.

Being too clean also can be a liability for kids since dirt’s benefits are skin-deep as well. Researchers at the University of California School of Medicine, San Diego, found that a common bacterial species that lives on skin, Staphylococci, triggers a pathway that helps prevent inflammation, improving skin’s ability to heal.

Why Contact with Dirt Can Facilitate Learning

Thanks to Friendly Bacteria Mycobacterium Vaccae

According to a four-year study that examined approximately two million children under the age of 18, antidepressant use is on the rise in kids, with the fastest growing segment found to be preschool children aged 0-5 years.

An increasing number of experts are recognizing the role of nature in enhancing kids’ mental health. It’s easy to see the effect when you watch children play outside. Kids are different when they’re outdoors. Free of school pressures and harried schedules, they relax and simply become kids. In fact, according to one study, children’s stress levels fall within minutes of seeing green spaces, making outside play the perfect antidote for an overstressed child.

Studies now also show that touching the earth has a powerful and positive effect as well. Making direct contact with soil—gardening, digging for worms, or making mud pies—has been shown to improve mood, reduce anxiety, and facilitate learning. In a study by Bristol University, Mycobacterium vaccae, or M. vaccae, a “friendly” bacteria found in soil, was shown to activate a group of neurons that produce the brain chemical serotonin, enhancing feelings of well-being, much in the same manner as antidepressant drugs and exercise. Interest in the study arose when patients treated with M. vaccae for another health issue reported increases in their quality of life.

Beyond raising mood, time kids spend in the dirt may be the best preparation for the classroom, according to researchers at The Sage Colleges in Troy, New York. They wondered whether, in addition to its antidepressant effect, M. vaccae may also have an effect on schoolwork. “Since serotonin plays a role in learning, we wondered if live M. vaccae could improve learning in mice,” says Dr. Dorothy Matthews, who co-authored the study. What they found was the bacteria did, in fact, significantly improve learning, and, in addition, the mice demonstrated fewer anxious behaviors.

“This research suggests that M. vaccae may play a role in anxiety and learning in mammals,” says Dr. Matthews. “It is interesting to speculate that creating learning environments in schools that include time in the outdoors where M. vaccae is present may decrease anxiety and improve the ability to learn new tasks.”

Getting messy is a win-win for children because it’s also FUN. Here are some wonderful ways to get started.

Be a Builder

Your children can make buildings of all shapes and sizes if they use sticks to create a frame and pack mud on to it—houses or forts perhaps, a castle with a moat, a stable to put toy horses in. If they also like the idea of large-scale public works, have them make a river by digging a trench in the mud or dirt. Then, add water as needed. Most importantly, build a dam to protect the town!

Be an Artist

Give your child a stick and a muddy surface to draw on. Mistakes are no problem; mud is a very forgiving medium. Just smooth it over and start again! Mud prints are fun too. Your child’s muddy hands and/ or feet can stamp cool patterns onto a sheet of paper. If you prefer to keep it simple, the sidewalk is another canvas. And then there’s sculpture. Mud balls can become out-of-season snowmen or abstract sculptures. If your child’s creation isn’t sticking together, just add more water.

Be a Biologist

Take a walk through your neighborhood or a local park so your children can learn which animals go under cover during rain and which come out in this type of weather. You might not have pigs nearby, but some dogs will happily wallow in a mud puddle if they have a chance. You may also see birds swooping down to take a bath.

This is also a fine time to study worms that surface to breathe when their burrows fill with water. Supply a magnifying glass so your children can get an even closer look. Then, enlist the kids in a Worm Rescue Squad. Ask them to move any worms they find on the sidewalk back to the dirt so they don’t dry out. Now, help them build a worm hotel.

Be a Chef

If you’re going to play in the mud, why not make some mud pies? If you have some old cake or pie tins, great. Otherwise, shallow plastic containers work just fine. Once the pies are “baked,” it’s time to make them beautiful! Encourage your children to scour the yard for pebbles, petals, and leaves that will make perfect decorations on top. Collect dirt, grass, leaves, twigs, and acorns in a large container, and you have a bountiful nature salad. Add some water, and it’s mud stew! (Remind small children to play with their dirt food, not eat it!)

Be a Gardener

Little hands love to garden! Get some kid-size gardening tools and let kids help mom and dad plant vegetables—it’s so exciting to watch them grow and it just might help kids eat more of them. Read “Growing Vegetable Soup” by Lois Ehlert for inspiration. Let kids choose and plant flower seeds or bulbs.

Spending time outside is great for kids, and studies show that getting dirty while they’re out there might be even better. With benefits to immune systems, hearts, and skin, as well as kids’ emotional well being and learning skills, doctors may well soon prescribe: “Make two mud pies and call me in the morning.”

Be a Camper

The Great American Backyard Campout sponsored by the National Wildlife Federation is an awesome way to introduce your children to the Great Outdoors. Every summer thousands of people across the nation get outside and connect with nature. It doesn’t matter whether you camp in your own backyard, with neighbors, in a local park, or campground; or whether you’re an old pro or new to camping. What matters is that you spend an evening outside enjoying the wonders of nature. Find resources at www.nwf.org/Great-American-Campout!

Article reprinted with permission of National Wildlife Federation www.nwf.org