Mixing toilet bowl cleaner and aluminum foil causes a chemical reaction that produces hydrogen gas. According to Newton Ask a Scientist, the typical reaction with this mixture is 6HCl + 2Al = 2AlCl3 + 3H2(gas).
Mixing toilet bowl cleaner and aluminum foil causes an exothermic reaction that produces a significant amount of heat. This mixture is sometimes used in producing homemade bombs, leading to serious consequences. In April 2011, three teens were charged with felonies after creating a bomb using these materials. In April 2013, a school resource officer charged Kiera Wilmot, a 16-year-old female student with no other disciplinary record, with possession and discharge of a weapon on campus after she mixed one of these bombs in an 8-ounce water bottle. The reaction was strong enough to force the top off the bottle. The Polk County School District expelled Wilmot.
The reaction between aluminum foil and toilet bowl cleaner produces aluminum chloride and hydrogen gas. When hydrogen gas mixes with oxygen, it becomes flammable. This reaction caused the explosion of the Hindenburg zeppelin in 1937. Breathing pure hydrogen is deadly. Aluminum chloride is the primary ingredient used in antiperspirants. It is an eye irritant and harmful to skin due to its acidity.