The ring around the bathtub is caused by soap scum an dirt. The ring can be washed off using bathroom cleaner.
Bubble bath residue and epithelial tissue.
When you bathe the dirt and soap floats off your skin and sticks to the side of the tub, leaving a ring when the water is drained.
soap scum sticks to the side of the bathtub witch causes bathtub rings to form.
Your bathtub. Go clean it.
Fluorine
stratum corneum
bathtub ring
The color of the ring that the cat leaves in the bathtub in "The Cat in the Hat Comes Back" is pink.
PINK
This might refer to the dirty ring left around a bathtub when someone soaks in a bathtub with soapy bubbles then empties the water. The dirty soap clings to the the sides of the bathtub leaving a ring mark of residue where the high water level was.
PINK