If your immediate reaction to cutting your finger open is to stick it in your mouth, know that you’re not alone. Wound-licking is an instinctive response not just in humans but in many animals: Dogs, cats, small rodents and primates all lick their wounds.
There’s a good reason for it, too. A 2008 study discovered that a protein in saliva called histatin not only helps kills bacteria—and therefore, prevents infections—but also accelerates the healing process, Wolverine-style (only, y’know, slightly slower). The study also found that wounds treated with saliva were almost completely closed after 16 hours, while untreated wounds remained largely open after the same amount of time. A study published in 2006, meanwhile, explained that an enzyme in saliva called lysozyme can attack the cell walls of bacteria to defend against infection.
None of this is news, of course: The introduction to a study published back in 1938 claims that, “It is well known that the addition of saliva to blood will accelerate its coagulation.” So wound-licking has generally always been regarded as a useful thing to do.
The problem, however, is that while our actual saliva is useful for treating wounds, there are millions of other spit-hopping bacteria in with it that can wreak havoc if introduced to a wound under the wrong circumstances—for instance, when your immune system is already down. A 2002 report recounts how doctors were forced to amputate the thumb of a diabetic man who fell victim to necrotizing fasciitis (that is, a rare flesh-eating disease, like a fast-acting leprosy: It can begin eating away skin tissue in as few as 12 hours and can be fatal absent urgent medical care) after licking a small wound.
Likewise, having a friend or a pet lick your wound can be similarly dangerous (and probably super uncomfortable, unless you and your buds are real close). That’s because everyone’s immune system is uniquely adapted to their own bacterial makeup, and being exposed to someone (or something) else’s can easily cause infection.
So what’s the major takeaway here? While licking your cuts and scrapes could theoretically help them heal, it’s a risky move. All in all, it’s best to stick to the safer alternatives: Soap, disinfectants and bandages. Not only is it more hygienic, it’s way less gross than slurping up your own blood.