We’re deep into the summer and as a parent you may be wondering what you can offer your kids that will leave a lasting impression. The answer could be as simple as letting them get dirty. I’m not alone in recommending this. A clever ad campaign for recreational vehicles (RVs) that began earlier this year reminds parents that what kids really want is their ‘wildhoods’ back. They want to get dirty, have fewer rules and experience the exhilaration of under the stars. If you’re hesitant to heed that advice then consider the science of . After all, the best legacy a summer vacation could give a child is a lifetime of strength.

There is quite a well-known article that appeared in Brain, Behavior, and Immunity that reports on research by Thomas McDade and his colleagues at Northwestern University. What they found was that people exposed to lower levels of microbes during their infancy were much more sensitive to the “pro-inflammatory effects of stress” as adults. In practical terms, what that means is that the more germs we experience as children the better our immune systems will be later in life at preventing physiological reactions that make us susceptible to becoming . Put simply, dirt makes us psychologically strong.

If we think about this like a preventative immunization, then giving kids a chance to get dirty (maybe even eat dirt) may be just what the doctor ordered for long term resistance to stress. Indeed, giving kids back their “wildhoods” is a great strategy for physical and psychological health.

Now contrast that advice to the growing number of grocery stores that provide sanitary wipes next to the shopping carts. While I sympathize with parents who are concerned for their children’s wellbeing, I think the microbiologists would warn that all that wiping is making our children very, very sickly. In fact the best thing we can do is let our children lick those grocery cart handles (unless you know for certain there has been an outbreak of SARS or similar deadly disease in your neighborhood).

It’s important to understand that an increasing number of studies like the one by McDade are linking the resilience of mind, body and spirit. Stress resistance is both psychological (what we think and feel) and physical (a healthy gut, it seems, will influence our ability to withstand stress). The same could be said of the . There is something calming about being out in nature. An article in Scientific American summarized the evidence that when hospitals work with landscape architects to build gardens for patients, or position patients with a view out over trees, they are likely to heal faster and use less pain . I’m inclined to believe that children with healthy doses of nature are less likely to have behavioral problems. Maybe that’s because they are more tired at the end of the day, more stimulated, or maybe it’s because there are fewer rules being imposed by over-protective parents who can’t seem to leave their kids alone long enough for them to make mistakes and figure out their own solutions.

I’ll admit I’m biased. Though science should never be based solely on an ‘n of 1’ (i.e., a single case study should not be the basis for scientific truth), I have to say that there is something that draws me out into nature. In fact, the idea for this blog came to me a few days ago as I bicycled to work along a converted railway line through a wooded area. A deer came out of the woods just in front of me and I slowed to watch it. The encounter, with the noise of the city in the background, was immensely calming. It was as if someone had reminded me to breath a little deeper. The experience lingered all day making the stress of deadlines a little easier to tolerate.

It’s a small example of what we all experience. Maybe it’s the perspective nature brings (think Henry David Thoreau and his time spent on Walden pond), or maybe it is the dirt that gets under our nails when we play outside that triggers our ability to protect ourselves from stress. Either way, with summer in full bloom, I’m going to do what I can to get my kids outside, then follow their lead and get dirty.