How often should you actually wash your jeans?

There is no number. The three groups of people who will confidently give you one are each answering a different question from the one you asked.

A dermatologist will say every two or three wears. A study everybody has heard about will tell you a student wore one pair for fifteen months and came to no harm. The denim trade will say as close to never as you can manage. All three are arguing in good faith, all three are right about the thing they are actually measuring, and none of them is answering “how often should I wash mine”.

The three answers, and what each is really about

The strictest comes from medicine. Dr Alok Vij at the Cleveland Clinic gives every two to three wears, and his reasoning is skin rather than fabric. Bacteria held against the legs by tight trousers can cause folliculitis, an acne-like rash that most people who have it assume is something else. A fungal infection picked up elsewhere can be carried to the groin or thigh by a pair worn again and again without a wash. That is a real mechanism, and it is why the tightest answer comes from a doctor.

The case for washing rarely rests, almost entirely, on one experiment. In 2009 a University of Alberta student named Josh Le wore a single pair of raw jeans for fifteen months and asked his textiles professor, Rachel McQueen, to swab them before he washed them for the first time. The counts were high, worst at the crotch at somewhere between eight and ten thousand bacterial units per square centimetre, and completely ordinary: normal skin flora, nothing harmful, no E. coli.

The half people forget is the better half. He washed them, wore them a further two weeks, and swabbed again. The counts came back to roughly where they had been. McQueen said she had expected them to be far lower. So what the experiment actually shows is not that unwashed jeans are clean; it is that the bacteria on jeans is yours, and it returns almost immediately whatever you do. Which is a good reason to stop deciding this on bacteria. It is also one person experimenting on himself, so it is suggestive rather than evidence, and it is quoted as though it were the latter roughly every time.

The third answer belongs to the denim industry and has travelled furthest. In 2014 the chief executive of Levi’s, Chip Bergh, said he had not washed the pair he was wearing in a year, and the line went everywhere. He has since clarified that he never told anyone not to wash their jeans and that his objection was to the washing machine specifically. The clarification went nowhere at all, which is the usual fate of clarifications. Worth noting too that the trade is interested twice over here: it sells longevity, and it is not the party who has to sit next to the result.

The freezer does nothing

Since it comes up every single time. A night in the freezer does not sterilise jeans: a domestic freezer is nowhere near cold enough, and not by a small margin. And if it were, freezing still is not cleaning. Everything a day of wear put into the fabric is in the fabric the next morning, only colder.

Never washing costs you the jeans

This is the part that ought to settle the never-wash school, and what gives it weight is that it comes from inside. Denimhunters exists to write about raw denim for people who care about fades, which makes it the opposite of a hostile witness, and it is blunt: infrequent washing of denim you wear a lot makes the fabric brittle and prone to tear in exactly the places it has faded. The crotch. The honeycombs behind the knee. You wear through those much sooner than you expect to.

The mechanism is not mysterious. Wear folds sharp creases into a stiff fabric, and every movement after that concentrates the abrasion on the same fold. Add the oils and grit that any garment collects and the fold hardens instead of relaxing. Washing releases it. Cotton also happens to be one of the few fibres that is stronger wet than dry, by something in the region of ten to twenty per cent, because water bonds into the cellulose rather than attacking it. The water is not what is wearing them out.

The one thing the never-wash rule claims to protect is the thing it costs you.

The specific form of the rule, wait six months before the first wash, was popularised by a brand. Denimhunters, again on the enthusiast side of this, calls six months a convenient number, and points out that what makes a high-contrast fade is how much you wash rather than a date in a diary. Nothing happens on the day. If you want the contrast, wash less; that is the whole of the trade-off, and it is a trade-off rather than a rule.

Raw, selvedge, sanforized

Three words get used as though they were one word, and they are not, and which of them applies to your jeans decides more about washing them than any interval could. Anyone about to tell you never to wash denim should be able to say which they mean.

Raw means the denim was never washed after it was dyed. Nothing has been done to soften it, fade it or shrink it, so it arrives stiff and dark and does all of its ageing on the person wearing it. That is the appeal, and it is the only one of the three words that is about washing at all.

Selvedge is a fact about the loom. A shuttle loom weaves a narrow bolt with a finished edge down each side, the self-edge, which is the clean seam with the coloured line you see when a cuff is turned up. It says nothing whatever about whether the jeans have been washed. You can buy washed selvedge and you can buy raw denim with no selvedge in it, and a good deal of what gets called raw selvedge means only that the jeans were expensive.

Sanforized is the word nobody uses and the one that decides what happens when denim meets water. Sanforising is a mechanical pre-shrink from the 1930s: the woven cloth is fed damp through heated rollers and a rubber belt that compress it lengthwise, so most of the shrinkage is taken out before anything is cut. Almost all denim sold is sanforized, and a sanforized pair barely moves in the wash.

Unsanforized denim, sold as loomstate or, at Levi’s, as shrink-to-fit, has had none of that done to it, and it shrinks on first contact with water by a long way: on the order of a full tag size in the waist and up to eight or nine per cent in the length. Which is why the first thing that happens to a pair of those is not a wear but a soak, an hour in lukewarm water, before anyone finds out what size they actually bought.

Worth noticing what that does to the rule. A good number of the people telling you never to wash your jeans put theirs in a bath before they had worn them once, because the fabric gave them no choice. The purity was never quite there.

Jeans is not one garment

Which is what actually resolves this. A pair worn daily on a building site and an occasional pair of raw denim are two different objects sharing a word. One meets sweat, soil and rain and wants washing on a scale of days. The other is being worn precisely for what deferring the wash does to it. No single count can be right for both, and every count anyone has offered is right for one and wrong for the other. The number was never going to be found, because the question has two answers wearing the same name.

A trigger works where an interval cannot, because a trigger scales with use on its own. It is correct for someone in them on a building site and correct for someone in them on a Saturday, and neither has to do any arithmetic. That is why the jeans row in our schedule is the only one of the six without a number in it. We would rather the table came out uneven than bend a row to match the others.

The one worth explaining is sag

Smell needs no explanation. Sag does, because it is not dirt at all and washing fixes it for a different reason. Cotton gives where you move it: the knees, the seat, the thighs. Body heat and a day of bending relax the fibres into the shape you have been holding them in, and the fit goes with them. Washing takes them back. That is why a pair that has gone shapeless by Thursday fits again on Saturday, and it means half of what sends jeans to the machine is a fit problem being solved rather than a hygiene one.

And when you do wash them

Inside out, cool, and keep them out of the tumble dryer, which is where most of the damage attributed to washing actually happens. Beyond that, the garment’s own label decides it rather than we do. The tub with a number in it is the only part of the label that has to be obeyed; everything else there is the manufacturer telling you what it can survive.

If they are raw and the fades are the point, the method matters more than the frequency does, and it comes down to three things. Inside out, always, because the face of the fabric is the part you are trying not to abrade and because a drum will press vertical creases down a leg that has never had one. Turn the spin off if the machine lets you, for the same reason; better still, do it by hand in the bath, which is what the careful end of this has always done. And treat the temperature as a sizing decision rather than a cleaning one, because hot water shrinks denim and cold water holds the size you have got.

And most of the answer is not a wash at all. Airing them properly, a damp cloth on the mark rather than a cycle for the whole garment, a day off between wears so the cotton can recover its shape. That is the general case as much as the denim one, and it is the argument this guide is built on: the wash is the smallest part of looking after clothes, and the days in between decide how often you need it.