Okay but imagine Boyfriend!Sans and Boyfriend!Papyrus seeing you get a sunburn for the first time, not knowing what happens after.
It's not like they haven't done research on humans since coming to the surface, right? They know about a lot of weird little health quirks human bodies have, like how your hair will get greasy over time if not washed, or how you have to clip your nails or they'll just keep growing, or even the way your smell can changed based on the day or your diet.
Strange to them, but mostly normal. Mostly fine.
So you all hit the beach one weekend, and they know the shape of a sunburn. Papyrus packs extra tubes of sunscreen, probably five different SPF ratings, a few creams, a few sprays, and Sans will lazily smear some on your nose and call it a day while actually rubbing it into your back so you don't end up burned.
You end up burned anyways.
Because guess who forgot to reapply.
It wasn't like you meant to forget! You'd all just had such a good time it just sorta...slipped your mind.
Which is how you end up with a sunburn, shoulders and forehead taking the worst of it.
Sans and Papyrus are absolutely guilt stricken about it, the few days of your skin being too tender to touch making them absolutely more miserable than you are. Papyrus applies aloe gel to you like you're gonna shatter, and Sans is throwing his hoodies at you like you're meant to live in them now, and the sun, once their favorite thing to enjoy during summer time, has now become their personal enemy for hurting you.
A week passes, your skin heals, and all is fine. The skelebros are relieved, and the crisis is averted.
And then the peeling starts.
You're in the bathroom, shirt off, and pulling at the edges of a really, REALLY satisfying strip of dead skin, feeling itchy and relieved all at once. It's the good kind of peeling, where it comes away in fat strips and makes a satisfying noise every time. You're about to shower and scrub yourself down anyways, so you may as well enjoy it while you can.
Sans, in all his unknowing innocence, opens the door to come in, because personal space does not exist in this household and it never will.
"Sans, I'm about to shower," You give him a half hearted protest, looking at him with a playful glare over your half peeled shoulder, still holding a fat strip of skin in your fingers that's still connected at the curve of your arm.
Sans's sockets have gone completely dark.
He's stood rigid in the doorway, skull locked onto your shoulder. Then he turns to look at the other one. And then your forehead, which is slightly raw from where you'd already done that first.
"Love," He chokes out, his voice wrecked. "Love, what the fuck."
You blink, looking at him in confusion, "What? I'm just peeling, Sans," and then back down to your shoulder, and just start continuing to pull the dead skin off it, the strip growing longer in your hands with that satisfying noiseโ
Sans's gloved hand snaps around your wrist as he shortcuts right next to you, his eyelights back as thin, shaking pinpricks in his sockets in what you can only think looks like complete and total horror on his face.
"Paps. PAPS. PAPYRUS."
"Brother? What in all the stars are you up here shouting aboutโ"
Papyrus comes around the corner while you're protesting over Sans's grip on your wrist, mourning how the strip broke early, and also confused as to what the hell Sans is freaking out about.
Papyrus is frozen in the doorway, sockets flicking between your shoulders, Sans's face, your face, your PEELING FLESHโ
"Oh my Asgore."
Absolute pandemonium breaks out between the two brothers while you're suddenly being dragged to sit down on the toilet and handled like you're a bomb about to go off.
"PAPS GET THE KITโ"
"I HAVE THE KIT! I HAVE ALL THREE KITS! CALL THE 911 NUMBERSโ"
"DON'T TOUCH 'EM OH MY GODโ"
"IT'S COMING OFF IT'S ALL COMING OFFโ"
"I KNOW IT'S COMIN' OFF BRO I CAN SEE ITโ"
"GUYS!"
You shout over their panic and screaming, trying your best not to laugh, because they're very genuinely terrified for you, but god is it hard to keep a straight face.
"It's fine. This is normal."
They both look at you like you'd told them spaghetti was a fruit.
"Kid," Sans's voice is completely strained. "I'm no doctor, but I'm pretty damn sure skin's supposed to stay on humans, not come off."
"I CAN SEE IT COMING OFF YOU!" Papyrus practically wails, clutching his skull and doing tight little circles in the bathroom. "RIGHT NOW! IT'S JUST HANGING THERE! MENACINGLY!"
You really should get a reward for choosing, in that moment, not to laugh in their faces. You're a good partner. You do not laugh. Your voice is not that steady though, so points deducted for that one.
"It's called peeling, and it happens after a human gets a sunburn," You explain as calmly as you can to them both. "It's actually a really, really good thing."
The looks they give you mean they absolutely do not believe you for a single damn second.
"Look," You sigh, pulling out your phone, tapping into the search bar, and pulling up the first article you can find that explains the process, turning it to them both. "Too much UV damages the skin. That's what the sunburn was. SO, in order to make sure my cells don't turn into cancer, my body kills of the skin, it turns into this little peeling layer, and it sheds itself off. Kinda like a snake. It's a built in defense mechanism to keep me healthy after a sunburn."
Papyrus snatches the phone from your hands while Sans is basically vibrating in place, eyelights locked onto your shoulders while his brother frantically scrolls through the article.
"So...this is...healthy?" Papyrus asks slowly, still sounding unsure. "And all humans do this...'peeling'?"
You nod, breaking down how leaving it on can be itchy, and the shower scrub down would've gotten rid of most of it anyways. This part, which was the weirder part to explain, was just satisfying to do, because of said itchiness, and also just because it was...kinda fun. It was completely harmless, and a sign that your body was working the way it should.
Sans just collapses onto the bathroom floor, laughing helplessly with his face in his hands, a mix of relief and mild trauma, while Papyrus looks caught between curiosity and absolute mild horror.
You end up showing them how to peel the spots you can't reach. Papyrus discovers he absolutely cannot stand the sound, gagging as he throws his hands up and storms out of the bathroom to go 'MAKE SURE WE HAVE TEN MORE TUBES OF SUNSCREEN SO THAT YOU DO NOT EVER SHED LIKE A SNAKE EVER AGAIN'.
Sans though?
He's having a blast now that he's knows your skin isn't falling off and you're not dying.
His eye for detail given the work he does, and his thinner, pointed boney fingertips are perfect for getting the smaller, stubborn edges of dead skin you can't reach. He's made it his current mission to see how big of a piece he can make with each pass, showing them off and calling them your 'precious human shed', which is by far the grossest way to word it you've ever heard, and is exactly why it has you laughing until you're coughing.
He's a little disappointed when you finally run out, leaving behind small bits that just won't peel enough anymore and the slightly tender and fresh skin underneath.
Though he's still going to make sure to apply extra sunscreen on you next time you all hit the beach. He doesn't want another soul attack.
Papyrus? He might just dunk you in a whole tub full before you go.
Just to be safe.