"patch of skin" is correct and usable in written English.
You could use it in a sentence like "The doctor applied a bandage to the injured patch of skin."
In essence, laser tattoo removal is touching a wand to a patch of skin.
Why not some other patch of skin?
A patch of skin had ripped off her shoulder.
She turned her head and saw a heap of bloody rags and a patch of skin.
One day she noticed a scaly red patch of skin on her right arm.
He turned over a melon, which had a butter-yellow patch of skin where it sat in the dirt.
They then gave the volunteers microscopic wounds by peeling off a small, thin patch of skin with tape.
As the patient recovered on antiretroviral therapy to a CD4 count of 600, he developed a lighter-colored patch of skin.
You can see every wrinkle on his neck, every reddened patch of skin on his face, the flare of his nostrils and slant of his nose.
I notice a small, discoloured patch of skin on her hand, a wound from a beating that will never completely heal.
A brew of the material was then spread on a patch of skin that had been cut and then rubbed raw.
