The Chemistry of Laundry Pods

Click to enlarge

Laundry pods have featured in the news this week after cases of people eating them in what’s being referred to as the ‘Tide Pod Challenge’. In case you didn’t already realise that this is a pretty terrible idea, this graphic looks at the chemical reasons why you really don’t want them anywhere near your mouth.

Laundry pods are small plastic packs filled with washing detergent. The outside of the pack consists of a polyvinyl alcohol (PVA) film, which is soluble in water. In your washing machine it dissolves and releases the detergent.
 
The detergent is largely composed of molecules called surfactants. These include compounds like ethoxylated alcohols or akylbenzene sulfonates. Surfactants are molecules with two ends: one end loves water and readily dissolves in it, while the other hates it. To go into more chemical detail, one end can form hydrogen bonds with water and dissolve, but the other can’t. It’s this duality of character that allows surfactants to get your clothes clean.
 
Water-hating (hydrophobic) ends of the surfactant molecules won’t dissolve in water, but will dissolve in oily substances. In your washing machine, they dissolve in the grease and dirt on your clothes. Meanwhile, the water-loving (hydrophilic) ends of the molecules are only too happy to dissolve in water. This leads to the surfactant molecules clustering around dirt and grease particles, water-hating tails sticking into them, and water-loving heads allowing the clusters to dissolve in water and wash away.
 
Surfactants don’t do all the dirty work. Some stains are tougher to shift – biological washing detergents contain enzymes which can help break these stains down. Optical brighteners, compounds which absorb UV light and re-emit it as blue light, are also added. This gives a whitening effect, keeping your white shirts appearing yellowish.
 
It might seem obvious that eating this combination of compounds isn’t be a great idea. However, it seems that hasn’t stopped some people, either accidentally or on purpose. So what are the dangers?
 
Eating laundry pods is particularly risky since the detergents are at a higher concentration than in liquid detergents. They are highly alkaline; just as highly acidic substances can cause burns, so too can very alkaline ones. If you eat a laundry pod, you run the risk of burns to your throat and stomach from the high concentration detergent they contain. As they pop in your mouth, they can also be accidentally inhaled – definitely not good for your airway and lungs either.
 
In addition, eating them can also cause breathing problems. Why exactly this is is currently unclear. It seems that in some laundry pod formulations, a sedative effect is seen when they are ingested. This can lead to drowsiness and breathing difficulties. It’s been speculated that a solvent used in the pods, propylene glycol, might contribute. Alternatively, it might be an unknown effect of certain ethoxylated alcohols.
 
To dissuade small children from eating the pods accidentally, pod manufacturers started adding a bittering agent, denatonium benzoate, to the plastic film. This is the most bitter chemical compound known, and is also used for the same reason in antifreeze. It might even provide further dissuasion to those considering eating the pods deliberately.
 
If you do ingest the contents of a laundry pod, manufacturers’ recommendations are to seek medical attention immediately. Some countries have National Poison Helplines which can also give advice. Of course, it’s simpler to just not eat them in the first place!
 

 

 

 

 

Note: the original structure of denatonium benzoate had a missing nitrogen atom. This has now been corrected in the current version of the graphic.

Enjoyed this post? Support Compound Interest’s graphics on Patreon!

The graphic in this article is licensed under a  Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. See the site’s content usage guidelines.

 

References & Further Reading