TL;DR
Soap slime is not dirt. It is bar soap partly dissolved in standing water, mixed with the mineral scum that forms when soap meets hard water. That means no cleaner fixes it permanently -- drainage does. Wash the dish weekly with hot water and a brush, use a dish that drains, and keep the bar out of the spray so it can dry between uses.
What the slime actually is
Two things are happening at once.
Dissolved soap. A wet bar sitting in a shallow dish loses material into the water around it. That water evaporates slowly, leaving a concentrated soap slurry that stays soft and slippery.
Soap scum. Where the water is hard, calcium and magnesium react with the fatty acids in bar soap to form an insoluble film. That is the gray, chalky, sticky layer that grips a dish and does not rinse off.
Add skin cells, body oil, and dust, and you get a film that feels like slime, smells faintly sour after a while, and can grow mildew in a humid bathroom.
Liquid soap dispensers create a different version of the same problem: a crust around the pump and a ring where drips land.
The underlying issue -- water that has nowhere to go -- shows up all over a bathroom, which is the running theme of our guide to cleaning the personal items you use every day.
How do you clean a slimy soap dish?
Take the dish to a sink, rinse the slurry off under hot running water, then scrub it with a brush and a drop of dish soap. For hardened soap scum, soak the dish in one part white vinegar to two parts hot water for twenty to thirty minutes, scrub, rinse, and dry it completely.
The weekly clean
1. Remove the bar and empty the dish.
2. Rinse under the hottest water the material tolerates. Heat is what softens soap film. Cold water simply pushes it around.
3. Scrub with a brush and dish soap. A dish brush or an old toothbrush for the corners and any drainage holes. Grooves and ridges hold the most.
4. Soak in a vinegar solution if scum has hardened. One part white vinegar to two parts hot water, twenty to thirty minutes. Vinegar dissolves the mineral part of soap scum, which plain soap will not touch.
5. Scrub again and rinse thoroughly.
6. Dry it completely before the bar goes back. A dry dish stays clean far longer than a wet one.
Never combine vinegar with bleach or any chlorinated cleaner. That mixture releases chlorine gas. If you want to use a bleach-based product on a dish, rinse away all vinegar first and give it time, or simply pick one and stick with it.
What material your dish is decides the method
Ceramic and porcelain. Tolerate hot water and vinegar well. Dishwasher safe in most cases. The easiest to keep clean.
Glass. Same as ceramic, and scum shows more clearly on it.
Plastic and acrylic. Warm water rather than hot, since heat warps thin plastic. Avoid abrasive powders, which scratch and give scum something to grip. Acrylic in particular hazes with alcohol and some solvents.
Silicone. Very easy. Flexible enough to bend and peel scum off, dishwasher safe, and it dries fast.
Natural stone, including marble and travertine. Do not use vinegar. Acid permanently etches natural stone, leaving dull patches that cannot be polished out at home. Use a pH-neutral cleaner and hot water only, and dry the dish after every use.
Wood and bamboo. Never soak. Wipe, scrub quickly with a soft brush and mild soap, rinse fast, and dry standing on edge. Oil it occasionally to keep the grain sealed.
Metal. Stainless steel tolerates soap and vinegar but not chloride bleach, which pits it. Chrome-plated and wire dishes rust at the contact points, which is the same failure covered in how to clean a shower caddy and stop rust rings.
Why does soap turn to slime in the dish?
Because the bar sits in water that cannot drain. Soap dissolves into that standing water and forms a soft slurry, and hard water minerals react with the soap to make a sticky scum. The fix is a dish that drains and dries, not a stronger cleaner.
Choosing a dish that stops the problem
The cleaning is a symptom. The dish is the cause.
Drainage holes or open slats. Water needs a way out. A solid dish with a rim is a reservoir.
A raised platform or ridges. Keeping the bar out of any water that does collect makes an enormous difference.
Slatted or wire designs. Maximum airflow underneath the bar.
A draining soap saver mat. These sit under a bar in an existing dish and let air circulate.
Magnetic soap holders. The bar hangs from a small magnet embedded in it and dries completely on all sides. Effective, and they eliminate the dish entirely.
Location. Move the dish out of the direct spray of the shower. A bar that gets rinsed every time somebody showers never dries and dissolves twice as fast.
Habits that keep it clean
Rinse the dish whenever you notice buildup rather than waiting for the weekly clean. Ten seconds under hot water prevents the hardened stage.
Keep a small brush in the bathroom. The job is trivial when the tool is right there.
Let the bar dry between uses. A soap dish outside the shower, or on the far side of the tub, does the same work as any product.
Run the exhaust fan during showers and for fifteen to twenty minutes after. Bathroom humidity is what turns a damp film into mildew.
Use up soap slivers rather than stacking a new bar on the remains of the old one. That combination stays wet indefinitely.
If the water is hard, expect scum regardless. A monthly vinegar soak on non-stone dishes keeps ahead of it. The same mineral issue drives the buildup in how to clean a slimy toothbrush holder and under the mat in how to clean a rubber bath mat and its suction cups.
Source: U.S. Geological Survey information on water hardness and its household effects
Cleaning up the surface underneath
The dish is only half of it. The counter, ledge, or tile under a soap dish collects the same film.
Wipe it when you clean the dish, and check what the surface is before choosing a cleaner. Natural stone counters and cultured marble need pH-neutral cleaners, not vinegar. Quartz takes no bleach, no abrasives, and no high heat. Glazed tile handles almost anything, but the grout between tiles is porous and stains.
A ring left too long on stone can etch permanently, which is a repair rather than a cleaning job.
FAQ
How do you get soap scum off a soap dish?
Soak the dish in one part white vinegar to two parts hot water for twenty to thirty minutes, then scrub with a brush and rinse thoroughly. Vinegar dissolves the mineral part of soap scum that plain soap cannot touch. Do not use vinegar on natural stone dishes, which it permanently etches.
Why does my bar soap go slimy in the dish?
Because it is sitting in standing water. Soap dissolves into that water and forms a soft slurry that never dries out. A dish with drainage holes, a raised platform, or open slats lets the water escape and the bar dry, which stops the slime without any cleaner at all.
Can you put a soap dish in the dishwasher?
Ceramic, porcelain, glass, and silicone dishes usually can. Plastic dishes may warp on a hot cycle, and natural stone, wood, and bamboo should never go in. Check the underside for a dishwasher safe mark, and hand wash anything you are unsure about.
How often should you clean a soap dish?
Once a week for a dish in daily use, with a quick rinse whenever you notice film building up. Weekly cleaning prevents soap scum from hardening, which is the difference between a ten-second rinse and a thirty-minute soak.
Can you use vinegar on a marble soap dish?
No. Vinegar is acidic and permanently etches marble, travertine, and limestone, leaving dull patches that cannot be polished out at home. Use hot water and a pH-neutral cleaner instead, and dry the dish after each use so scum has less chance to build up.
What kind of soap dish does not get slimy?
One that drains and lets air reach the bar: slatted dishes, wire holders, dishes with holes and a raised platform, or a magnetic holder that suspends the bar entirely. Keeping the dish out of the direct shower spray matters just as much as the design.
Small fixes like this add up, but a bathroom that is genuinely clean top to bottom takes real time. If you would rather hand that off, get a quote or read more about house cleaning services.