Drugstores are struggling to keep glue – yes, ordinary white schoolhouse glue – on the shelves. Parents are keeping a wary eye on the upholstery. And children are selling bags of an odd, glue-based concoction recently banned by at least one elementary school in Kansas.

This can only mean one thing.

Slime is back.

It goes by several names, and the recipes vary, but the main ingredients are glue, water, and borax. The result is a gloriously gloppy mess, customizable with glitter, food coloring, and other add-ins.

Alicia Hebert's first clue came a few months ago, when she wanted to do the laundry in her Chadds Ford home but could not find the detergent. Her daughter Hana, 10, turned out to be the culprit – as detergent contains borax, also known as sodium borate.

"I go into her room, and there's this slime everywhere," Hebert said. "I had to put a stop to that."

She now allows slime in uncarpeted areas of the house -- but Hana needed more glue. The family struck out at Target, Walmart, and Michaels, then finally ordered some online, Hebert said.

They have plenty of company. The makers of Elmer's Glue report a slime-related increase in sales in the second half of 2016, with a particular spike in December, when retail sales of liquid glue more than doubled, compared to the same month a year earlier. Hoboken, N.J.-based Newell Brands has stepped up production to meet the demand, and has been impressed by the evidence of creativity on social media sites, spokeswoman Caitlin Watkins said.

"We've seen a variety of slime recipes oozing through cyberspace over the past few weeks," she said.

The company posted its own version a few days ago, calling it "glitter gak." On Instagram, there are 1.7 million posts with the hashtag #slime. And for the 12 weeks ending Jan. 22, unit sales of glue were up 15 percent at major retailers compared to the same period a year earlier, according to IRI, a Chicago-based market research firm.

But why? A lingering effect of the 2016 Ghostbusters reboot? A yearning for simpler times?

The resurgent craze has prompted amusement among educators who have been making it for years. Pattie DiTomaso, who conducts science demonstrations at the Franklin Institute, said the enduring appeal lies in its simplicity.

"In this digital age, it's basic stuff," she said. "It's good chemistry."

Under another name, the science museum also has used the substance for a lesson on the immune system, said Mickey Maley, assistant director of public programs. A few years back, someone made a big model of a nose to simulate how it filters pollen and other allergens, complete with black pipe-cleaners to represent nose hairs.

Particles of pollen were represented by confetti, blown through the "nose" by a leaf-blower. Initially, most of the confetti blew right through. But when slime was added – dubbed "mucus" for this purpose – the nose blocked confetti much better, Maley said.

"The mucus was pouring out of the nose," he said. "Great visual."

Slime also is a great way to teach chemistry, said Mickey Sarquis, a professor emerita of chemistry at Miami University in Oxford, Ohio.

The basic principle is simple, she said. Glue is basically a mixture of water and polyvinyl acetate, a type of polymer. These long, stringy molecular chains slip and slide past each other like cooked spaghetti in a pot of water, she said.

But when you add borax, it forms chemical bonds between the "spaghetti" much like the rungs on a ladder, she said. The polymer strands can no longer slip and slide, and the result is gooey and stretchy. (Technical term: a cross-linked polymer.)

Sarquis taught teachers how to use slime as a classroom tool, though back in the 1980s she called it "gluep,"  and published several related papers in the Journal of Chemical Education. Pro tip: when mixing borax powder in water, do it in a ventilated area, she said. (see recipe at end)

For Sarquis, the term slime meant a different substance, in which the glue was replaced by polyvinyl alcohol. Not to be confused with Slime, the commercial product made by Mattel in the 1970s, which contained a substance called guar gum.

Sarquis devised classroom demonstrations in which students joined hands to mimic the long chains of polymers. Once, she did a slime workshop with Amish students in Indiana, and posed a question that she immediately regretted.

"You don't ask a bunch of farm kids what it reminds you of, because you'll get answers you don't want to hear," she said.

Others riding the slime train include a blogger at babycenter.com, who wrote that her child's Kansas elementary school had banned slime because it was a distraction, and Good Housekeeping, which chimed in this week with its own recipe.

Though to us, it seems a bit like bad housekeeping. Getting the stuff out of your carpet is murder.

Not to worry, said Miami's Sarquis. If you catch it before it dries, slime can be removed with a few dabs of vinegar – an acid that dissolves the cross-linked chemical bonds.

Linda Vertlieb, who blogs at www.frugalphillymom.com, likes the activity for her children, Sophia, 9, and Alex, 4, because of the inexpensive ingredients, and advises stocking up on glue during back-to-school sales.

The low cost helps for those slime-makers who are capitalists as well as chemists, said Hebert, the Chadds Ford mom.

Her daughter's friends have been selling it to each other for $1 per container.

But not Hana.

"She thought that wasn't fair," Hebert said, "so she gives it away."

How to make your own slime

Measure 1 tablespoon of glue (such as Elmer's) into a cup. Add 2 teaspoons of water and stir well. Add 2 teaspoons of borax solution (that's 1 tablespoon of borax dissolved in a cup of warm water) and stir the mixture.

Your slime will be sticky for about a minute. Pull it out of the cup and knead it with your fingers until it feels drier and less sticky. Store it in a sealed bag, in the refrigerator.

SOURCE: Franklin Institute