Of the many, many things we're not supposed to snack on, perhaps the most common forbidden food is silica gel.
This tiny packet pops up in packaging for everything from TVs and guitar cases to sunscreen and snack foods.
So why is silica gel everywhere?
And what would actually happen if you ate it?
Found in the Earth's crust.
Silica, also called silicon dioxide, is typically mined as raw silica sand, which is then washed dried, sifted and chemically treated.
Once manufacturers ensure each grain is uniform, the processed sand gets mixed with sodium carbonate, then heated and combined with an acid that links the silica particles into a jelly-like matrix.
This matrix gives the material its porous structure, which stays stable after being washed and dried into hard glassy beads.
The final product is chemically identical to the sand you might find on a beach.
The only difference is that porous structure.
Inside each silica gel bead is a massive microscopic network of tunnels.
This dramatically increases the surface area of each bead with a single gram of silica, offering over 700 square meters of surface area.
But this space doesn't stay empty for long.
The silicon dioxide molecules that make up the gel are held together by polar covalent bonds, which attract other polar substances, including water.
So when silica gel is placed in a humid environment, the water in the air is drawn to the bead's surface.
From these surface pores, the water vapor is then pulled inside the grain through a process called capillary condensation.
Each grain can hold up to 40 of its own weight in water, allowing a standard 5-gram packet to hold roughly 2 grams of liquid.
And since this liquid is held inside the bead's internal network, even fully saturated silica doesn't feel wet to the touch.
This ability makes silica gel a desiccant, a type of substance used to keep things dry.
But these beads can suck up more than just water.
Silica attracts ammonia, sulfur dioxide and a handful of other gases, making it useful in gas masks and other filtration systems.
The pace of this process depends on the environment.
In a very humid, enclosed space, a packet could reach its saturation point within a day or two.
But this could take up to a week in a moderately humid environment.
Either way, silica gel beads functionally last forever since you can dry them out in a hot oven.
These abilities and silica's prevalence in Earth's crust have made it the planet's most popular commercial desiccant, since we started mass-producing it in 1919.
At home.
It keeps snacks crispy and extends their shelf life, ensures pills and vitamins stay dry and captures any stinky scents from your cat's litter box.
Museums use silica gel in exhibit cases to prevent metal artifacts from rusting and preserved animals from growing mold.
And in outer space.
A form of silica gel called aerogel is used to insulate rovers from extreme temperatures and capture high-velocity comet dust for study back home.
But what about what silica gel would do to you if you successfully swallowed a packet?
The answer is not much.
Those do-not-eat warnings have more to do with packets being choking hazards than any silica-specific concerns.
Besides, your body has so much liquid in it.
Even if the packet did suck up the standard 2 grams, you could replenish that much and more with a single glass of water.
And since silica is chemically inert, your body won't break the gel down into something toxic.
That said, downing larger quantities of silica gel would be unpleasant.
Its moisture-wicking properties could dry and irritate mucous membranes along the digestive tract, resulting in diarrhea and an upset stomach.
Worse still, some silica is coated with cobalt chloride to indicate moisture levels, and that compound actually is toxic.
But assuming your silica snack is of the standard variety, you should survive the ordeal.
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