They sometimes use so much that even by the time the final rinse kicks in, suds are still visible in the machine. Occasionally.... the suds are so great that bubbles cascade out of the top of the machines and make small children squeal!
It may also occur if a laundry detergent is added that is not meant for use in that particular type of washing machine. A typical example of this is when a customer brings their top-loader detergent from home and uses it in a laundromat's front loader.
So, why is oversudsing not a good thing? Well, laundry detergent contains more than one ingredient - and each one has a job to do. The one we are going to focus on right now is the good old surfactant.
The word surfactant is an abbreviation of the words "surface-active-agents." Surface active agents have a unique chemical structure which makes them able to interact with two different types of surfaces, for example - oil and water.
Surfactants are shaped roughly like a tadpole. Now, imagine placing a load of greasy tea towels in a washing machine and adding detergent. As the drum fills with water, the water repelling tail of the surfactant goes mad attaching itself to the grease and dirt suspended in the water. Meanwhile, the machine’s tumbling motion helps by tossing your laundry about and breaking down the dirt and grease into smaller, easier-to-remove pieces.
During the rinse cycles, the water molecules attach themselves to the opposite end of the surfactant (the head) and help pull the dirt and grease away from the tea towels. During the final spin – water flushes away the surfactant molecules with all their dirt and grease attached to them.
The problem is – if you use too much detergent – a washing machine’s cycle cannot possibly flush away all the dirty molecules. By using too much detergent you have effectively created a situation where four, six or eleventy-six rinses would be needed in order to rid your clothes of the surplus surfactants and their dirty little tails.