Based on the shape of a gas mask Castrillo's design was strapped to Lady Gaga's head with buckle and had goggle-like frames around the eyes with a mesh-covered hole for the mouth. The chin piece was decorated with curved cables that protrude in different directions.
"When I designed this piece I got inspired by gas masks, but wanted to make something a little bit different, so I included cables and I left free the eyes area with a big opening," Castrillo told Dezeen.
"That's because when I designed it I was thinking to be worn by a woman, so she could show the eyes enough."
To contrast with the gas mask's more sinister connotations, Castrillo hand-made the mask from a bright pink leather material.
"My work is always inspired by horror films as it was my favourite entertainment when I was a child," he explained.
"The concept was something industrial, a bit gothic, but still different as that kind of colour reminds me of something sweet. I like mixing different concepts as in this case, a gas mask, that is something scary with a concept of something visually sweet."
The pink mask was paired with a technicolour dress made by fashion designer Iris van Herpen from laser-cut multi-coloured duchess satin, which was hand-stitched onto a corseted body.
"The otherworldly gown radiates in fringed coils that drip off Lady Gaga's body like raindrops," said Iris van Herpen.
Lady Gaga wore the ensemble to accept her artist of the year award, as one of five outfit changes she wore during the MTV Video Music Awards (VMAs) on 30 August.
Castrillo, who has previously made designs for Madonna and Marilyn Manson, said that as face masks become a more common part of everyday life due to the coronavirus pandemic, they are in turn becoming seen as a fashion accessory.
"I remember when some years ago saw people on the underground wearing masks I thought, wow, so strange ," he explained.
"We are all wearing masks, covering a part of our faces," he added. "We all need them to protect ourselves and others, so I think definitely it's now a fashion accessory."
Other examples of masks made to be fashion accessories include a design with detachable chains plated in silver and gold, which German jewellery designer Saskia Diez created to appear less medical, and an expandable and reusable face mask Petit Pli made from recycled plastic bottles.
Photography courtesy of Iris van Herpen.