TL;DR
The fill decides the method. Down and polyester pillows can be machine washed two at a time on a gentle cycle and dried on low for one to three hours with dryer balls. Memory foam and latex must never go in a washer or dryer -- agitation tears them apart. Every pillow type fails the same way when it is not dried completely: mildew inside where you cannot see it.
What is inside the pillow?
Look at the tag before anything else. There are four common fills and they have almost nothing in common.
Down and feather. Natural fill, washable, needs mechanical agitation while drying to re-loft.
Polyester or fiberfill. The most common and most forgiving. Washable, dries fastest.
Memory foam. A single solid piece of viscoelastic foam. Never machine washable.
Shredded foam or latex. Sometimes machine washable if the pieces are loose in a removable cover, but the foam itself is not.
Also check whether the pillow has a removable zip cover. That cover almost always washes normally even when the insert does not.
Down and feather pillows
Wash two at a time so the machine stays balanced. Use a front loader or a top loader without a center agitator -- the post tears seams and shreds feathers.
Use a small amount of down-specific wash, or a mild liquid detergent at half the usual dose. Down is hard to rinse and leftover detergent causes clumping.
Run a gentle cycle in warm water, with an extra rinse. Use a moderate spin.
Dry on low heat for one to three hours with clean dryer balls. Stop every thirty minutes, take the pillows out, and knead the clumps apart by hand. This is the step that returns the loft, and skipping it leaves a flat, lumpy pillow.
Dry until completely dry. Squeeze the pillow at the center. If it feels cool or dense, keep going. The same rules apply to down jackets, and how to wash a down jacket at home covers the drying process in more detail.
Never use fabric softener or dryer sheets on down. They coat the clusters and the loft loss is permanent.
Polyester and fiberfill pillows
The easiest category.
Wash two at a time on a gentle cycle in warm water with a normal but not generous detergent dose. Add an extra rinse. Dry on low or medium heat with dryer balls, checking every half hour and fluffing by hand.
Fiberfill dries considerably faster than down, typically under an hour and a half. It also degrades faster -- repeated washing gradually breaks the fibers down, so a fiberfill pillow that has been washed several times and no longer holds shape is simply at the end of its life.
Memory foam and latex: never in a machine
This is the one hard rule in the category. A washing machine will tear solid foam apart, and a dryer will damage or scorch it. Once foam breaks internally it never recovers.
Clean memory foam this way instead:
Vacuum both sides with an upholstery attachment to pull out dust and skin cells.
Spot clean stains with a cloth barely dampened in water with a drop of mild detergent. Blot, do not soak, and do not rub. Foam absorbs water readily and releases it very slowly.
Rinse-blot with a second cloth dampened in plain water to lift the detergent.
Air dry completely, flat, in a room with moving air, out of direct sun. This can take a full day. A fan speeds it up considerably.
Deodorize with baking soda. Sprinkle it over the surface, leave it several hours, and vacuum it off.
Never wring, twist, or fold a wet foam pillow. Never put it in the sun to speed drying, since UV degrades foam.
How often to wash pillows, and when to replace them
Wash pillows two to four times a year, and wash pillow protectors and cases far more often -- protectors monthly, cases weekly with the sheets.
A pillow protector is the single most effective thing you can do here. It takes the body oil and sweat that would otherwise soak into the fill, and it washes easily. Body oil is also what causes the yellowing you see on old pillows, and the same residue behaves the same way on shirt collars, which is why how to remove body oil from collars uses the same treatment logic.
Most pillows need replacing every one to three years depending on type. The fold test is a reasonable check: fold the pillow in half and let go. If it stays folded rather than springing back, the fill has collapsed and washing will not bring it back.
Source: American Academy of Sleep Medicine general sleep hygiene guidance
Dust mites live in bedding, and washing reduces their population. That is a reduction, not elimination, and it is not a treatment for any allergy or condition -- that is a conversation for a doctor.
Load size and balance
Two pillows is the right number for most machines. One pillow alone slams to one side during spin and throws the machine off balance. Three or more usually pack the drum so nothing rinses.
Bulky items generally need room to move, and how full a washer load should be covers why crowding defeats both washing and rinsing.
If your machine is small, a large-capacity machine at a laundromat is a better tool for pillows and comforters. And while the bed is stripped, it is a reasonable moment to deal with the mattress underneath -- how to clean a mattress covers that job.
FAQ
Can you put pillows in the washing machine?
Down, feather, and polyester pillows can go in a washing machine, two at a time, on a gentle cycle. Memory foam and solid latex cannot -- agitation tears the foam structure and it does not recover. Check the care tag before assuming.
How do you wash a memory foam pillow?
You do not machine wash it. Vacuum both sides, spot clean stains with a barely damp cloth and a drop of mild detergent, blot with clean water, and air dry completely away from sun and heat. Baking soda handles odor.
Why does my pillow smell after washing?
It is not fully dry. Moisture trapped in the middle of the fill produces a musty smell within a day or two. Put it back in the dryer on low with dryer balls until the center feels warm and dry, and expect that to take longer than you think.
How often should pillows be washed?
Two to four times a year for the pillow itself, monthly for a pillow protector, and weekly for the pillowcase. A protector absorbs most of the body oil that would otherwise reach the fill and makes the pillow last considerably longer.
Do yellow stains on pillows come out?
Usually not completely. The yellowing is oxidized body oil that has been through repeated heat cycles, and it bonds to the fibers. An oxygen bleach soak in hot water helps on cotton-cased polyester pillows, but expect improvement rather than a full reset. A protector prevents it going forward.
When it stops being one job and becomes every room, house cleaning services are the wider answer.
Pillows are one of those items people skip for years and then replace, when a wash and a protector would have doubled their life. If bedding and laundry are part of a household workload that has stopped fitting your week, help is available. Every home is different, so the real number depends on size, condition, and what you want covered. Get a quote and we will walk you through it.