If the absolute worst were to happen and a nuclear conflict erupted close to where you live, it's vital to know what to do. And what not to do.
Simmering nuclear tensions in the past week have thrown apocalypse survival tactics back into the spotlight, and with them, a rather unusual emergency factoid: if a nuclear blast happens, you really, really should refrain from using hair conditioner.
It might sound a little crazy, because after all, priorities people! As one online commenter put it, "like Imma be worried about bounce and body when the sky is literally on fire".
They've got a point.
But the reason we shouldn't condition our hair is less to do with the blast wave of fiery annihilation – in which case it's sadly probably too late to do or not do much of anything – and more about the invisible, insidious consequence that lingers in its wake: nuclear fallout.
The spectre of this dangerous, radioactive dust raised its ugly head last year, after escalating rhetoric between North Korea and the U.S. saw the former threaten to surround the Pacific island and US territory of Guam with an "enveloping fire" of missile attacks.
In response, Guam's Office of Civil Defence issued a fact sheet on how to prepare for an imminent missile threat, including a recommendation to "not use conditioner in your hair because it will bind radioactive material to your hair".
The exact same warning appears on the U.S. government's own disaster preparation site, Ready.gov, and according to radiation safety expert Andrew Karam, it's sound advice.
This is because, following a nuclear blast, hair conditioner could make it easy for tiny radioactive particles in the air to stick inside microscopic crevices that cover the surface of each strand of human hair in between scales of hair protein.
"[Hair] can come apart during the day like a pine cone," Karam explained to Angus Chen at NPR.
"Radiation contamination particles can get between those scales."
If you're worried about shampoo, don't be. Shampoo is fine, as is soap, and they're even recommended by the authorities.
That's because shampoo and soap are used to wash things off our skin and hair. Hair conditioner, on the other hand, contains compounds called cationic surfactants and polymers that act like a kind of glue to stick hair protein scales down.
That effect makes hair cosmetically smooth, giving it all that resplendent body and bounce we see on TV ads – but when radioactive particles are slowly settling down over you and your family, the last thing anybody needs is glue on their hair.
"Unlike shampoo, conditioners are meant to stay behind on your hair," cosmetics chemist Perry Romanowski told NPR, and that characteristic is why we should also be cautious of using other sticky personal care products in a fallout scenario.
"Skin lotions or moisturising lotions or colour cosmetics that have oils - these go on your skin and can attract dust or radiation particles from the air. So that would be a concern."
Of course, there's a lot more to know about surviving a nuclear bomb than just how to adjust your hair grooming regimen – including knowing what emergency supplies you should have, and the kinds of places where you should and shouldn't seek shelter.
But if the worst happens and you think your skin or hair has been contaminated by radioactive dust, just make sure to wash it off thoroughly, as quickly as possible – and above all, don't panic.
"Radioactivity is like changing a diaper," Karam said.
"You don't want it on you, but if you do get it on you, just wash it off and go on with your day."