There have been several documented cases of aerosol cans containing dry shampoo exploding when left too long in hot cars.
Dry shampoo is type of shampoo that reduces hair greasiness without the need for water. It is typically in a powder form, often delivered through an aerosol can. It is generally a mixture of corn starch and alcohol, which absorbs excess oil on the scalp and hair. Many women celebrate it as a time-saving, miracle product.
But according to chemists who have studied these types of explosions, all dry shampoos are not equal.
In a 2019 case involving a Missouri teenager who left an aerosol can of dry shampoo in the center console of her used Honda Civic, which then exploded - blowing out the sunroof and destroying the center console area - the exploding bottle was an Equate brand, Walmart's in-house line of beauty products. Interestingly, there was a second bottle of Dove brand dry shampoo in the same center console that did not explode.
Experts who commented on this particular case suggested that the most likely explanation is that the car got too hot for the canister.
Ingredients in the Equate bottle included propane and butane, flammable chemicals that become more dangerous under pressure. The denatured alcohol, which forms the base of the dry shampoo, is also flammable. The propane and butane ignited in the pressure filled, hot canister and created a bomb-like situation that blew the sunroof off of the car. The bottle did have a warning that said the product is flammable and "may explode if heated."
If you or someone you know keeps dry shampoo in their bag or in their car, be cautious. That innocent looking bottle of shampoo may require a little extra care so it doesn't cause a serious accident.