The answer is skin that's fully intact and unbroken. It's the body's first line of defense against bacteria, viruses, and fungi.
The mouth, nose, and mucous membranes are all real entry points for pathogens — and so is any break in the skin, whether that's a scrape, a cut, or inflammation. That's exactly why a fresh nick during a shave changes the safety picture and calls for something like a styptic product to close it back up fast.
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