The Hindu festival of Kumbh Mela is currently underway in India. As part of the event, millions of pilgrims will take a cleansing dip in the confluence of the Ganges, Yamuna and the mythical Saraswati. Inspired by this headline, we splash into a whole bathtub of stories about the science of cleaning. We find out why it’s so important to prevent contamination of other planets and moons, and how space scientists keep things clean.

Next up, we discover how our brains clear out harmful toxins while we snooze.

And is there any truth in the saying, ‘tidy house, tidy mind’?

Finally, Marnie ponders whether it’s possible to be too clean, or if being a bit grubby is okay. Presenters: Marnie Chesterton, with Affelia Wibisono and Andrada Fiscutean Producers: Alice Lipscombe-Southwell, with Dan Welsh, William Hornbrook and Imaan Moin