Instagram is a place for photo ops and makeup experiments, which means that sometimes people post photos of looks you would not wear outside. A prime example of that is the new trend of putting glitter directly on your tongue. It's called Glitter Tongue, obviously.
But as with most things young people do on social media, it has adults worried. When you put stuff on your tongue, you might swallow it! And glitter is not a food, no matter how tasty it looks.
According to the Daily Mail, swallowing glitter can make you constipated, put unhealthy bacteria in your stomach, and make your poops more interesting (that last fact comes from me, a non-scientist). It's plastic. There are edible glitters on the market now, but you have to order them special. And even if you don't intend to leave the house with the glitter on your tongue, it's pretty difficult to scrape all the material out of your mouth after your photo shoot. Anyone who has tried to clean up after an arts and crafts session knows that glitter will follow you for an eternity.
So maybe it's not worth it no matter how cool it looks.
Though it does look cool.