Oozing Pumpkin | Science Experiment

Oozing Pumpkin - A jack-o'-lantern that oozes foam out of its mouth, nose and eyes will be a great addition to your Halloween party. It’ll give your family and friends “pumpkin” to talk about!

Love Steve Spangler Science’s “Elephant Toothpaste” demonstration? Our foaming pumpkin is a Halloween-themed spin on one of our most popular science experiments. Best of all, this pumpkin science experiment will fit right in with your Halloween party plans and will put you way ahead of the “carve!” With a few simple materials right from your home, you can make an awesome foaming ooze that seeps from every opening of your jack-o’-lantern’s face. Call it a puking pumpkin and you’ll immediately add a bit of grossness to this experiment that will definitely pique kids’ interest. It’ll bring bloodcurdling squeals of excitement and looks of disgust from the faces of your partygoers. Best of all, it all benefits science and produces a great learning opportunity that shows kids (and adults) how chemical reactions work!

Experiment Materials

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  • 12% Hydrogen peroxide ("V40" at hair salons)
  • Liquid dish soap
  • Food coloring
  • Package of dry yeast
  • Small cup (fits inside your pumpkin)
  • Dish or cup for mixing
  • Very warm water and stirring spoon
  • Small, carved pumpkin with lid
  • Gloves and paper towels for clean up
  • Large plastic trash bag
  • Tongs (optional)
  • Safety Glasses
  • Adult supervision

Experiment Videos



Cover your lab space with the plastic bag. (This makes it easier to clean up your space when you’re finished.) Fill a small cup with about 2 tablespoons (30 ml) of 12% hydrogen peroxide. NOTE: This cup needs to be small enough to fit inside your carved pumpkin. Cut out some of the pumpkin flesh under the lid if you need more space. Also, make sure there’s a flat spot on the floor of the pumpkin so the cup is stable.


Add a squirt of dish soap to the hydrogen peroxide.


Add some food coloring to give your foaming pumpkin a nice effect. Give the solution a stir with the spoon.


Dump the yeast into the other cup. Use all of it.


Add 4 tablespoons (59 ml) of very warm water to the yeast and stir it completely. If the mixture is too thick, like a goo, add a little more warm water to thin it. The yeast needs to pour quickly so you want it runny.


Open your jack-o’-lantern and carefully lower the hydrogen peroxide solution into the pumpkin. Don’t tip it over or you’ll have to start over. Some kitchen tongs may be useful to do this step.


This is the moment of truth! Quickly pour the yeast solution into the hydrogen peroxide and replace the top of your jack-o’-lantern. It may take a few seconds. Once the reaction starts, the foaming, spooky result is well worth the wait!

How Does It Work

How Does It Work?

Remember treating scraped knees or a cut with hydrogen peroxide? H2O2 is the chemical formula for hydrogen peroxide and shows that it is made up of two hydrogen atoms and two oxygen atoms. H2O2 looks like ordinary water (H2O), but the addition of that extra oxygen atom turns the molecule into an extremely powerful oxidizer. The hydrogen peroxide found at the grocery store is a 3% solution, which is safe to touch yet is powerful enough to kill bacteria, viruses and fungi on surfaces.

The hydrogen peroxide used for this demonstration is four times stronger than the over-the-counter variety you can buy at the store. Low percentage hydrogen peroxide (3%) is great at home; it will not, however, produce the massive amount of foam seen in this effect.

The secret to this reaction is the catalyst, which is the yeast mixture. The yeast used in this experiment is the exact same stuff that makes bread rise; it is actually a single-cell fungus. Yeast is the secret ingredient that speeds up the decomposition of the hydrogen peroxide. This catalyst releases the oxygen molecules that are contained in the hydrogen peroxide molecule. When H2O2 decomposes, it breaks down to form water (H2O2) and oxygen (O2). The soap bubbles that erupt from the pumpkin are actually filled with oxygen.

As this reaction takes place, you’ll also see water vapor (yes, water vapor) rising out of the erupting foam. This shows that the reaction is exothermic, meaning that it gives off heat during the decomposition. As the bonds break between the H2O and O2, they release energy in the form of heat. Perform this oozing foam reaction in a cup and then feel the sides of the cup. They’ll be warm!

Take It Further

You have options! Not only can you add dish soap and food coloring to the hydrogen peroxide for mountains of bubbles, but you can also add a shot of our Glow Powder. This powder creates a really cool, glow-in-the-dark effect that will be perfect for your Halloween party. The keys to this effect are (1) to have a UV (ultra-violet) light source on nearby and (2) to do it in the dark. Now you get gobs and gobs of foam, plus it all glows with a creepy, yellow-green ghoulish light! Pumpkin volcano, a puking pumpkin, foaming pumpkin: Whatever you call this pumpkin science experiment, it is one fun activity to perform around Halloween at home or in your classroom!

More Halloween Science Fun 

Halloween is the perfect time to perform some of Steve Spangler Science’s best Halloween-themed experiments and activities at home or as a fun science class activity. Don’t miss our other Halloween party ideas, like Boo Bubbles, our Spooky Halloween Drink (also known as witch’s brew) or our fake blood recipe that will create some ghoulish good fun. From food science to chemical reactions, our pumpkin science activities and other great Halloween activities will have them howling with delight! There’s more science fun, too! If you loved our foaming pumpkin experiment, don’t miss our other chemistry experiments and food science experiments at Steve Spangler Science. For more activities that you can do at home, visit our online experiment library for dozens of hands-on experiments for kids of all ages!

Safety Information

CAUTION: Always be careful not to touch the foam with bare skin. Always wear safety glasses and protective gloves. Remember to cover your demo surface with a plastic drop cloth for easy clean-up. Everyone will want to touch the foam that gets made, but you must keep eager fingers away. This is just in case some of the hydrogen peroxide did not react completely with the catalyst. You don’t want anyone to get a hand burned or skin stained from touching the foam just after it’s made.

All of the “aftermath” from this reaction is safe to gather up in a plastic bag and either throw away in the trash can or wash down the drain.

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