Your mouth is weird. You may not have really thought about it, but the skin on the inside of your cake hole heals incredibly quickly, compared to, say, cuts on your knee or that gash on your back. It’s not really been clear why, though, but a new study – spotted by Gizmodo – injured 30 healthy humans to find out.

The team, led by the National Institute of Arthritis and Musculoskeletal and Skin Diseases, made tiny wounds on the inside of their cheeks, and others on their arms for comparison. They watched as they healed over time; skin samples were taken, and the molecular machinations of the samples were looked into.

The mouth wounds seemed to be taken over by the healing process immediately after they were formed, but the arm wounds were slower to recover – as expected. Not only that, but there was considerably less scarring going on in the mouth, something you’ve probably never really appreciated considering it’s a little tricky to see.

Writing in Science Translational Medicine, the team explain that there was a far larger number of up-regulated genes in the skin samples relating to skin repair days after the injury was inflicted. In other words, the genes that influence skin healing were still far more switched on than they were at the site of the inner cheek injury further down the line. This matches up neatly with the longer healing period for the skin wounds.

At the same time, the team spotted that transcription factors were consistently up-regulated in the oral wounds. Now, transcription factors are proteins, and by binding to DNA, they can turn specific genes on or off, so to speak.

It appears that they were switched on not just when the injury took place in the mouth, but beforehand too.

Think of it this way: The healing mechanism is always active in the mouth, as if it’s on red alert. This isn’t the case in the skin, where the big red button has to be pressed to begin the healing process.

In order to double-check their findings, the team turned to mice with skin wounds. By making sure some of the transcription factors were switched on more than they otherwise would be, the researchers found that healing was enhanced.

Although this study represents a key advance for the field, plenty more questions about the variability in how our body parts heal themselves remain.

It’s not clear, for example, why some organs of ours can regenerate – like the liver – which means it’s returned to its normal state, whereas others – like our eyes or heart – can only patch up the damage in imperfect repairs. Even when we are able to regenerate required tissue, other animals, like salamanders, certainly have us beat: They can regrow entire lost limbs, and it seems this ability, although hypothetically possible in humans, was lost long ago.

Nevertheless, this paper hints at a future where we can make use of the unique genetic fingerprint within our mouths to fix external wounds that heal far more slowly, or not at all.

It’s going to be more complicated than that, though. A recent review noting that the scar “microenvironment”, the person’s immune system, the type of cells present, and the inflammatory proteins all have a role to play.