How Men and Women Detect Dirt

It is an ongoing struggle in our family home. My wife is constantly telling our teenage son to clean his room, going so far as to bring him the mop, bucket, rag and surface cleaner. Isn’t that nice of her? He asks, (not so) innocently enough, why his room needs cleaning. “Because it stinks”, is her reply. It probably does smell to her, but it’s very unlikely that he detects his own body odour in the room, and to be honest, while I am aware of a faint smell of ‘teen spirit’, it doesn’t bother me very much. If push came to shove, I probably wouldn’t care whether he cleaned his room or not.

She also sees the dust and accumulation of dirt on the floor, which he barely notices, leading to a rather bizarre discussion – debate really – along the following lines:

Her: “It’s filthy in here. Look at the dust!”

Him: “What dust?”

Her: (Walks to the bookshelf and drags her index finger across the eye level shelf and then raises it to him). “This dust! And clean the floor!”

Him: “Why?”

Her: “It’s dirty. Look!” (Points out what looks very much like a soft drink spill that has had several days to dry and harden on the tile floor near his desk)    

I describe this discussion as bizarre because it seems like a communication between two different species with a completely different set of sensory organs. My wife can see, smell, and feel the dirt in my son’s room, but he seems completely oblivious to any sensory input of this kind. How can this be?

Domestic grime and muck that would cause a typical woman to gag, is hardly even noticed, and more easily tolerated by the typical man. Not surprisingly then, research indicates that husbands and wives hold very different views about when and how often things need to be cleaned around the house, and in this case all arrows are pointing in exactly the same direction – she has higher standards than he does. She wants a pristine domicile, but he’s happy if it is ‘just clean enough’. She sees intolerable amounts of filth where he barely notices any, which brings us to a rather obvious question. How do you know when something is dirty, or more precisely, how do you determine when something needs cleaning? As it turns out, men and women have different approaches and use different kinds of sensory input to determine whether something exceeds their filth thresholds and filth tolerance levels.

Before we begin, let me be clear here. Filth thresholds and filth tolerance levels are not the same. The filth threshold is the point at which something begins to seem dirty – the point at which the filth first becomes noticeable.  Women notice filth before men. They have a lower filth threshold than men, which may lead to them doing more cleaning around the house, but this is not as big a sticking point for relationships as you might think. The filth tolerance level, on the other hand, is the maximum amount of filth that can be endured in the family domicile before you start to go completely mental.

So, the filth in my son’s bedroom didn’t even exceed his minimum threshold – he didn’t see or smell the anything. But the very same room exceeded my wife’s maximum tolerance level. Not only was she aware of the filth – it pushed her right over the edge!  Women freak out sooner than men when it comes to grime, and this is potentially a big problem if husbands take over the cleaning duties.

Do men and women react to filth signals differently? The answer may seem simple enough, until you consider the various senses involved in filth detection. When it comes to identifying dirt the senses of sight, smell, and touch play rather obvious roles. Things look, smell, and feel (i.e., a sticky floor) dirty.  Sound is also sometimes involved, as in the various noises your shoes or feet make when you walk across a dirty surface (i.e., crunches on kitchen floors, sloshes on bathroom floors, etc.). Taste, as it turns out, is almost never involved in filth detection for fairly obvious medical reasons.

Now it is easy to try to rank the senses in turns of importance in identifying dirt, but such an exercise would ignore the complex ways the various senses interact in the psychology of filth detection.  For instance, odours are obviously importance filth signals around the house. Bad smells tell us that something needs to be cleaned. But what, exactly? Here we need the supporting evidence of some other sense. We must either see the source of the smell, or sometimes feel it, as in the sticky spot on a kitchen counter, before we know what to clean.

The half-eaten banana my son left in his bedroom six days ago will give off an odour indicating that something needs to be cleaned.  But until I find it dropped behind his desk (sight), or worse yet, step on it (touch), I can’t clean the mess. So smell is sort of a theory of filth, whereas sight and touch constitute cold, hard facts.

There are, of course, exceptions to this rule, as in locating the source of the stench in the fridge. Here the sense of smell alone can do nicely on its own if a specific item has ‘gone off’, though the testing process is rarely pleasant, and is sometimes a source of dread leading to astonishing intervals of procrastination. You’ve got to take a sniff of every item in the fridge until you find one that makes you gag. No wonder people put off this cleaning task.  And perhaps not surprisingly, refrigerators are the one domain where husbands are driven to action by smell alone. The tolerance for rotten food stench may be a lot higher for men, but they will eventually clean an excessively smelly refrigerator, at least until they find the offending item(s).

Then we have the situations where two senses provide conflicting evidence – the classic example being the mysteriously sticky kitchen floor.  It looks clean, but even after you mop it with a powerful concentration of surface cleaner, making it smell clean too, it retains the annoying sticky feeling. Do you mop it again? With a more powerful cleaner? Which sense do you trust in determining whether the floor is acceptably clean?   

We are not likely to resolve such important matters here, but at least we have the foundation for understanding gender differences in filth detection. Research suggests one fairly obvious distinction between husbands and wives when it comes to determining whether something needs cleaning. It is simply a matter of differential weighting of the various senses.

For men, something requires cleaning because it looks dirty. Men have to see the dirt before it occurs to them that something needs cleaning. One housekeeping book targeted at men is rather explicit in specifying this rule of thumb – “If you can’t see it, don’t clean it.” That sticky kitchen floor is fine to a man because it looks clean. A somewhat smelly bathroom is perfectly acceptable to a man, unless there is an obvious stain associated with the smell. As one man succinctly put it:

“Once I see it, and it’s visible as a layer, yes. But I’ve got quite a high tolerance level to it.”

For women, the other senses are more likely to come into play in determining whether something is dirty, even if it looks perfectly clean. Smell is an obvious candidate, and keep in mind that a considerable amount of research indicates that women have a keener sense of smell than men. Might this not be used to detect filth in the absence of visual cues? Women may still rely on a second sense like sight to verify the source, but the bad smell alone will exceed her cleaning threshold long before he pays any attention to it.

As an aside, smell is also a cue for assessing whether a cleaning product has done the job. Cleanliness is inherently hard to assess by sight alone, whether it’s a little one’s school short, a bathroom floor, or the inside of an oven. Most cleaning products are based on what we marketing types call credence attributes.  Consumers must largely take on faith that the product does what it’s supposed to do. The standard marketing claim that a kitchen or bathroom cleaner ‘kills 99.99% of germs” is an obvious example of something that consumers must take on faith. How, exactly, could they verify this? In order to convince consumers of credence attributes marketers often provide a second attribute, easily detectable by consumers, that largely serves as a surrogate for the first – in this case smell. If an oven, floor, or school shirt smells a certain way, then it simply must be clean.  Once again, smell serves only as a theory or surrogate for cleanliness.

There is also another criterion for cleanliness that goes beyond the senses – time.  Yes, time.  Much of the cleaning that takes place around the house occurs simply because of the interval of time since its last cleaning. Things get dirty over time, or so the theory goes, and women more than men are likely to keep track of how long it’s been since the carpet has been vacuumed. More generally, women may view housecleaning as something to be done on a periodic basis, whereas men are more likely to clean only when something is obviously dirty.

The ‘elapsed time’ criterion for when something needs cleaning simply doesn’t resonate with men the way it does with women, which is perhaps why housework books targeted toward men dismiss recommended cleaning frequencies on the labels and instruction manuals provided by manufacturers. One book on domestic labour scoffs at the idea that any man should be expected to adhere to a fixed schedule of cleaning the fridge. Only an intolerable amount of stench bordering on a new weapon of chemical warfare will provoke the typical husband to search for the no so recently departed item of sustenance.  

So, women rely on a more complex combination of multi-sensory cues in deciding that some part of the house is indeed dirty. If we can be more precise here, while men and women are likely to place a similar emphasis on sight cues, women are more sensitive to smell, touch, and time cues when deciding that something needs to be cleaned.