The youngsters are headed back to school... the weather is about to change... and flu season is fast approaching.

With fall on the horizon, you've got to brace yourself for all the germs that are about to start flying out of people’s noses and mouths.

Yuck!

Now, you know that keeping your hands clean is one of your best first-line defenses against getting sick – not only from the germs you might be carrying, but also from the germs you might pick up from somebody else.

But according to a new study, if you rely on hand sanitizer to do the job, you could be UPPING your risk of an infection, rather than cutting it down.

See, some of the worst germs out there are learning to outsmart alcohol-based hand sanitizers -- and that's allowing one of the most common drug-resistant SUPERBUGS to spread like wildfire.

In the study, Australian researchers analyzed bacterial samples taken from hospitals over nearly two decades (1997 to 2015) to see how they responded to the alcohol used in hand sanitizers.

And when the researchers zeroed in on Enterococcus faecium -- which is a strain of bacteria that typically lives in your gut but often spreads rapidly in healthcare settings -- they found that the bacteria collected after 2010 were 10 TIMES more tolerant to the alcohol than bacteria collected before 2004.

That means that over the years, these bacteria have figured out how to SURVIVE in alcohol for longer and longer periods.

Translation: That squirt of hand sanitizer will do zip to kill them!

Now, if your system is strong and healthy, E. faecium probably won't harm you.

But if you're on the older side... and your immune system is vulnerable... this "poop bug" can cause everything from sepsis (a.k.a. blood poisoning) to UTIs and more.

And since it's resistant to many of our most powerful antibiotics, it's no wonder that E. faecium is a growing threat, killing more than 1,000 American patients every year.

Now, you may think that if you're nowhere near the hospital, "washing" your hands with hand sanitizer is perfectly adequate to protect you from the germs that you're exposed to everywhere from public restrooms to the grocery store.

But who's to say that THOSE bugs aren't learning to outfox hand sanitizers, too?

More research is needed, but if you want a surefire defense against even the nastiest germs, your best bet is to take the time to wash your hands with plain ol' soap and warm water.

Not even the pathogen C. diff -- which causes deadly diarrhea and isn't killed by hand sanitizer -- can survive a good lather and scrub.

Just make sure that you're not washing up with an antibacterial soap that contains triclosan -- because studies have shown that triclosan can also give rise to drug-resistant strains of superbugs.

And if you're in a public restroom, choose paper towels rather than one of those hands-free dryers... because these devices can blow more of those poop bugs all over your just-cleaned hands.