Halloween Chemistry: Foaming Skull

Creating this exothermic reaction produces a large volume of foam that will creepily ooze out of a Halloween prop.

Experiment performed and video footage recorded by Andrea Champagne. For additional spooky fun, see how we made colorful flaming pumpkins.


Observe these safety precautions:

  • Wear safety goggles and gloves for protection. The strong hydrogen peroxide can burn skin and eyes.
  • Concentrated hydrogen peroxide can bleach fabric. Wear clothing that can get stained, or don a lab coat to protect your clothing.


To make a foaming skull, you will need:

  • A surface covering, such as an opened plastic kitchen trash bag
  • A containment pan, such as a rimmed cookie sheet or cat litter pan, to contain the foamy mess
  • ½ cup hydrogen peroxide, HO, at least 6%, which you can buy at a beauty supply store
  • 2 tbsp. water, approximately; warm
  • 1 package rapid/quick rise yeast (we suggest having more than one packet on hand in case you’d like to repeat the experiment)
  • 1 tsp. food coloring, any color
  • Liquid dish soap (a few drops; we used Dawn)
  • 2 cups or small bowls—one should have a pouring spout, or you will also need a funnel
  • A plastic or resin skull (look in your local store’s Halloween decoration aisles); you will need to cut or drill out the eye sockets, nostrils, and a hole in the top center of the skull (you may need a hole in the bottom of the skull, too, depending on the size of the skull’s base and the size of the container holding the yeast slurry. Alternately, you can use a carved pumpkin; save the top/stem to plug the top opening)
  • Tape, such as duct tape, that is at least 2” square or large enough to cover the hole in the top of the skull, or use the cut out piece of the skull attached to a cork to make it look seamless.


  1. Place the opened trash bag on the surface where you will perform the experiment.
  2. Place the cookie sheet or cat litter pan on top of the trash bag.
  3. In the first cup (the one that has a pouring spout), place the hydrogen peroxide, liquid soap, and food coloring; swish it gently to mix the ingredients.
  4. Place 2-4 tablespoons of water into a small microwave-safe container and microwave at full power for 20 seconds.
  5. Empty one packet of rapid-rise yeast into the second cup.
  6. In the second cup, gently stir 2 tbsp. of warm water into the yeast. Use just enough water to make a free-flowing slurry. Allow this mixture to rest for 1 minute.
  7. Place the cup containing the yeast slurry into the skull.
  8. Pour the contents of the first cup (soap/peroxide/colorant solution) into the skull (if the cup has no pouring spout, place a funnel into the hole in the skull, and pour the contents into the funnel).
  9. Quickly tape over or plug the top hole of the skull and step back.

The yeast, activated by the warm water, absorbs the oxygen from the hydrogen peroxide; this degeneration of oxygen froths the dish soap. The reaction produces millions of minuscule bubbles, resulting in a massive volume of foam.

Other things to try:

  • Add more soap, up to 1 tablespoon, to make a denser foam but slower reaction
  • The skull used in the video is approximately 6” across; if you use a larger prop, be sure to scale up

Let us know how the #foamingskull experiment worked for you, and if you have a video, post a link in the comments.


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