My grandmother who got it from her mother, who herself got it from her mother, used to put Marseille soap in the sheets at the foot of her bed.

What intrigued me...

But I found the explanation for this strange custom: the mixture of vegetable oil has the virtue of preventing cramps and rheumatism.

how does it work?

Night cramps and rheumatism are generally due to a lack of intracellular potassium. Authentic Marseille soap contains potassium chloride. By placing it between his fitted sheet and the sheet at his feet, he will, thanks to the heat of the bed and the body, release this component. This will then be deposited on the epidermis and reduce pain.

My advice : Put the soap in a nylon stocking to avoid dirtying the sheets but also to avoid burning yourself by rubbing with the soap during the night.