They look like something you'd draw on an Etch-A-Sketch, but instead of using a screen, Sarah Beal makes these patterns on her skin. Then she watches as they disappear – just like the classic toy.

The 43-year-old has a condition called dermatographia. The slightest scratch can cause her skin to swell. It also allows her to create designs and words on her body which vanish within an hour.

Dermatographia is thought to be caused when the cells under the surface of the skin release histamines under the slightest pressure. This causes the skin to swell and triggers a type of allergic reaction.