Steam does the work. Boil a bowl of water with baking soda or lemon juice in it, leave the door shut while it cools, then wipe. The softening is what removes baked-on splatter — scrubbing is what damages the interior, and the cavity is painted or coated, not bare metal.

The method that actually works

Put the mixture in a microwave-safe glass measure — not a plastic tub, and not a sealed container. Microwave it until it boils.

Then stop and leave it alone. FSIS is explicit that the mixture should stay in the oven, door closed, until it cools. Opening the door straight away lets the steam out, which is the only thing actually working on the residue. Give it ten minutes and the splatter wipes off without pressure.

Wipe with a soft cloth or a clean paper towel. For anything still stuck, FSIS names baking soda, mild soap or dishwashing liquid — applied to the cloth, not sprayed into the cavity.

Two notes on the water itself. Vinegar is the version most guides teach, and it does work, but it is not what the federal guidance specifies and it leaves its own smell. Baking soda or lemon juice do the same job and deodorise at the same time.

Why boiling water in a microwave needs a little care

This is the part almost no cleaning guide mentions, and it is worth knowing before you boil a bowl of water on purpose.

Water heated in a microwave can become superheated — hotter than its normal boiling point without actually boiling. FSIS describes it as occurring most often in a very clean vessel, often one straight out of the dishwasher, or when heating room-temperature water. Liquids heat with internal hot spots, so a temperature above 212 °F can build an inch or two below the surface while the top looks calm.

The risk is that the liquid then boils over violently when something disturbs it — adding a spoonful of anything, or in rare cases just moving the cup. It is uncommon, but the precautions cost nothing:

• Use a vessel with sloping walls, such as a glass measuring jug, rather than a straight-sided mug.
• Leave a microwavable spoon in the vessel while it heats.
• Stir occasionally rather than heating undisturbed.

All three give the liquid somewhere to start boiling normally instead of accumulating heat past the point where it should have.

What not to use

FSIS is direct about this: no steel wool, no scouring pads, no abrasive cleaners, and no oven cleaners. The interior of a microwave is a painted or coated cavity, and every one of those strips the coating. Once it is scratched through to the metal underneath, the damage is permanent and the exposed metal can arc.

Oven cleaner deserves its own mention because the packaging invites the mistake. It is formulated for the enamel inside a conventional oven and it is far too aggressive for a microwave cavity. If you clean both appliances on the same afternoon, keep the products separate — the fan-assisted oven guide covers what belongs in the other one.

FSIS also suggests checking the manufacturer’s manual first, and notes that some makers recommend unplugging the oven before cleaning it to reduce the risk of shock. That is worth doing if you are going to be wiping near the control panel.

The parts most guides skip

The cavity is the easy bit. Four other things collect grease and almost never get touched.

The turntable ring

The plate usually gets washed; the roller ring underneath it usually does not. It collects a film of grease that makes the plate drag and squeak. It comes out and goes in the sink with the plate.

The door seal and hinge edge

Splatter dries in the lip around the door where it is hard to see. Wipe along the seal with a damp cloth rather than digging at it — the seal is part of what keeps microwave energy inside the cavity, so it should not be scraped or pulled at.

The vents

Over-the-range models pull cooking air through a grease filter underneath, and countertop models have vents on the back or side. The filter is a real maintenance item on the first kind. Metal mesh filters go in the dishwasher or a hot degreasing soak.

The charcoal filter, on recirculating models

If a microwave vents back into the room rather than outside, it has a charcoal filter that cannot be washed — charcoal works by adsorption and once it is saturated it is finished. It is a replacement part, typically every six to twelve months depending on how much you fry. This is the item people are usually missing when a microwave still smells after a thorough clean. The same logic applies to charcoal filters in a range hood, and recirculating hoods work the same way — the ductless range hood guide explains which models use them.

Getting rid of smells

A lingering smell after cleaning usually means one of three things, and they need different fixes.

Residue you have not found yet is the most common — check the ceiling of the cavity, which is the surface nobody looks at, and the underside of the turntable. A lemon-juice steam is the direct treatment: the acid and the steam work on the residue and the citrus covers what is left.

A saturated charcoal filter is the second, and no amount of cleaning the cavity will fix it.

Burnt-on residue is the third. If something has actually scorched, the smell can persist through several cleans and a bowl of water left in overnight with the door closed will pull a surprising amount of it out.

How often

FSIS frames it as maintenance rather than a schedule: remove spatters and spills as they occur, so residue does not dry on. That is the honest answer — a thirty-second wipe after a spill removes the need for the steam treatment entirely.

Failing that, a steam-and-wipe once a week keeps an averagely-used microwave from ever needing anything harder. If you routinely reheat uncovered, make it more often; covering the food is the single change that reduces the work most.

Common mistakes

Opening the door as soon as the timer stops is the big one. The steam is the active ingredient and letting it out immediately means you are back to scrubbing.

Spraying cleaner directly into the cavity is the second. It runs into the vents and behind the panel where it cannot be wiped out. Put the product on the cloth instead.

Using an abrasive pad on a stubborn spot is the third, and it is the one that does permanent damage. If the residue is not moving, repeat the steam rather than increasing the pressure. If the coating is already scratched through to bare metal the appliance is past cleaning, and a convection toaster oven covers most of the same jobs better if you are replacing rather than repairing.

The fourth is cleaning the cavity and stopping there when the smell was never coming from the cavity. Check the filter before repeating the clean.

How This Guide Was Put Together

The method, the quantities, the list of what not to use and the superheating precautions all come from the USDA Food Safety and Inspection Service’s guidance on cooking with microwave ovens, which covers cleaning and the hazards directly. Nothing here was measured in a kitchen.

Two things could not be established. FSIS gives no interval for how often a microwave should be cleaned, only the principle of removing spills as they happen, so the weekly figure above is a practical convention rather than a sourced recommendation. And charcoal filter life varies by manufacturer and by how much frying a household does; the six-to-twelve-month range is what manufacturers typically state, not a tested figure.

Frequently asked questions

What is the best thing to clean a microwave with?

Steam from water with baking soda or lemon juice in it, then a soft cloth. USDA FSIS specifies 6 tablespoons of baking soda or half a cup of lemon juice per cup of water, and says to use baking soda, mild soap or dishwashing liquid on heavier soil.

Can you use vinegar to clean a microwave?

Yes, and it works, though it is not the formulation the federal guidance gives and it leaves its own smell behind. Baking soda or lemon juice loosen residue just as effectively and deodorise while they do it.

Why does my microwave still smell after cleaning it?

Usually because the smell was never in the cavity. Recirculating models have a charcoal filter that cannot be washed and needs replacing every six to twelve months. Failing that, check the cavity ceiling and under the turntable for residue you have missed.

Is it safe to boil water in a microwave to clean it?

Yes, with one precaution. Water can superheat past boiling point without visibly boiling, then erupt when disturbed. Use a sloping-sided glass jug, leave a microwavable spoon in it, and stir occasionally rather than heating it undisturbed.

Can you use oven cleaner in a microwave?

No. FSIS lists oven cleaners alongside steel wool, scouring pads and abrasive cleaners as things not to use. The cavity is a painted or coated surface and those products strip it, and exposed bare metal inside a microwave can arc.

Steam, wait, wipe. If it is not coming off, the answer is more steam rather than more pressure — and most of the mess is avoidable by covering food, which also settles the separate question of whether the packaging can go in at all.