Known as uguisu no fun in Japanese, nightingale droppings help the skin retain moisture and fight sun damage.

The nightingale might be most famous for its bewitching song, but the bird’s droppings are coming in at a close number two as spas across the world are opting to use the strange ingredient in skin treatments.

Known as uguisu no fun (nightingale powder) in Japanese, nightingale droppings were first used by geishas and Kabuki actors to remove their heavy makeup and whiten their faces. The substance has naturally high levels of urea, which helps the skin retain moisture, and guanine, an amino acid that leaves the skin luminescent and fights sun damage.

High-end spas have flocked to the ingredient and offer it in "Geisha facials" that range anywhere from $115 to $250 a treatment. Before being used on the skin, the droppings undergo ultraviolet sanitation and the substance is ground into a fine white powder. Then, the musky powder is mixed with water and other ingredients to create a mask to be brushed onto the skin.

Want to see if the treatment really works? Try it at one of these spas:

While we couldn't track down any spas in Japan that offer the treatment, residents say uguisu no fun can be found in supermarkets like any other beauty remedy.