You'd probably answer toilet bowl if you were asked what bathroom surface is swarming with the most harmful bacteria.
But according to the Daily Mail, there's another worthy contender for the disgusting title, and one that often gets forgotten about - your sink plughole.
Researchers found that putting hair, soap and dead skin down the sink doesn't just cause blockages, but can potentially pose a deadly threat.
Dangerous "biofilms" are easily created in the U-bend. These are considered to be the perfect environment for hundreds of lethal bacteria to thrive.
Washing chicken could immediately spell danger, if Salmonella escapes down the sink drain. This bug can be fatal for those with compromised immune systems.
The same issue exists with E. coli from ground beef, or contaminated produce. It can be life-threatening, but usually results in diarrhoea.
While regularly washing down hair and dead skin allows for a build-up of Fusarium solani, which can lead to permanent vision damage.
While urinary tract infections are also a possibility, as some studies have detected Enterobacter cloacae in water pipes connecting to the plughole.
If left untreated, these can harbour E. coli and salmonella, which can then become airborne and pass up through the plughole into the home.
They can be spread through "splash back", or through climbing up the biofilms that have been created in the drainpipe.
Only a trickle of water is needed to then allow the bugs to make their way into sinks and bathtubs, where they can infect humans.
The findings, derived from a scientific review, were conducted by researchers at the University of East Anglia. They are yet to be published.
What do the researchers say?
Writing in the report, they said: "Sink and bath drains and plugholes, within both the hospital and a domestic setting, are troubling reservoirs for microbes.
"Many of which are opportunistic pathogens and present threats to patients and house owners.
"There is a distinct lack of recent experiments focused on this microbial reservoir making future research into them paramount."
Domestic drains and plugholes include those found in the kitchen and bathroom sinks, baths and showers.
For shower and bath drains the environment would be warm, moist and saturated with waste such as hair and skin flakes.
Food prepared in the kitchen may be deposited down the sink, leading to a build-up of biofilms, the researchers said.
They particularly noted the Escherichia coli and Salmonella as being the biggest threats.
The report added: "These pathogens can easily... accumulate and proliferate within the kitchen sink drain."
What are biofilms?
Biofilms are thin layers of microorganisms, including bacteria, fungi, diatoms and algae, that stick together.
They like to grow on moist, nutrient-rich surfaces such as the bathroom blockages caused by hair, soap sulphates and oils.
Once fully formed, biofilms are notoriously difficult to get rid of as they become immune to the antibiotics contained in cleaning agents.
Buster commissioned the research, titled An Outline of the Microbiology of Domestic and Hospital Plugholes and Drains.
Edel Schultz, spokesperson for Buster, told MailOnline: "Prevention is much better than cure when it comes to biofilms and blockages."
'"These types of bathroom blockages are of course part of the status quo in a busy household and nothing to worry about in the short term."