Why You Should Never Put Washing-Up Liquid in an Ultrasonic Cleaner

Ultrasonic cleaners work via cavitation: high-frequency sound waves create millions of microscopically small bubbles in the liquid, which dislodge dirt particles from surfaces as they implode. Regular washing-up liquid is designed for manual washing with lots of friction, and foams heavily as a result.

This foam dampens the transmission of sound waves through the liquid and directly disrupts the cavitation effect – weakening the device's actual cleaning power rather than boosting it.

The instruction manuals of standard ultrasonic cleaners regularly include an explicit warning not to use flammable chemicals, acids, chloride-containing substances or ordinary household cleaners – instead recommending plain water or a concentrate specifically formulated for ultrasonic devices.

It's worth clarifying this point, since it's easy to mix up: for manually wiping glasses with a dampened cloth, water with a little washing-up liquid is, according to hygiene research, a genuinely effective method (see our bacteria article). But that's a different use case from using washing-up liquid INSIDE an ultrasonic device – there, the issue isn't whether washing-up liquid cleans effectively in general, but the specific way it disrupts cavitation through foaming.

Plain tap water is already sufficient for most applications, since the main cleaning effect comes from the cavitation itself, not from chemicals.

For more stubborn residue: a low-foaming concentrate specifically developed for ultrasonic cleaners, mixed at the ratio specified by the manufacturer.