In many homes, a pinkish residue frequently appears in bathrooms, particularly around drains, shower curtains, and tile grout.

Though it’s often mistaken for mold, this discoloration is actually caused by the bacterium Serratia marcescens.

This microorganism thrives in damp environments and feeds on fatty deposits found in soap and shampoo residues.

Dr. Karan Raj, a surgeon with the National Health Service (NHS), addressed this issue, stating: “If you’ve seen this pink slime lurking in your bathroom, it’s not mold—it’s bacteria.”

He further explained that Serratia marcescens “loves damp, moist places and enjoys munching on fatty deposits like those found in soaps and shampoos; hence why it likes to hang out in your bathroom.”

While generally harmless to healthy individuals, Serratia marcescens can pose health risks to certain populations. According to Infectious Disease Advisor, this bacterium “can be found in soil, water, plants, and animals,” and in homes, it “may be found in the corner of wet showers or wash basins, where it is visible due to the red-colored pigment (prodigiosin) it produces.”

For individuals with weakened immune systems—such as hospitalized patients, the elderly, or those with chronic illnesses—exposure to this bacterium can lead to infections in the urinary tract, respiratory system, or wounds. These infections can be particularly difficult to treat due to the bacterium’s resistance to multiple antibiotics.