TL;DR
Plastic containers hold onto grease, color, and smell because plastic is slightly porous and slightly oil-loving. Degrease with hot water and dish soap first, then treat stains and odors separately with a baking soda soak or a few hours in sunlight. Always pull the silicone gasket out of the lid, since that is where most smells actually live.
Why plastic keeps the smell of what was in it
Plastic is not the inert wall it appears to be. Its surface has microscopic pores, and it is oleophilic, which means it attracts oil rather than repelling it.
Oil carries flavor and aroma compounds. When oil soaks into the surface, so do the smells of garlic, curry, chili, and last week's soup. Water alone cannot reach them because water and oil do not mix.
Pigments behave the same way. Tomato sauce turns a container orange because carotenoid pigments are fat-soluble and travel into the plastic with the oil.
That is why the fix always starts with degreasing. Remove the oil and most of the smell and color come with it.
What is the right order for cleaning containers?
Degrease first with the hottest water your hands can stand and plenty of dish soap. Then treat any remaining stain or odor as a separate step with a baking soda soak. Then dry everything completely, gasket removed, before stacking it away.
Step one: degrease properly
Rinse out food debris right away. Residue that dries onto plastic bonds much more stubbornly than residue on glass or steel.
Wash with hot water and a generous amount of dish soap, using a soft sponge or a bottle brush for corners. Dish soap is a surfactant that grabs oil and holds it in the rinse water, which is exactly the job here.
For a greasy container, fill it with hot soapy water, cap it, and shake. Then let it sit fifteen minutes before washing. The dwell does more than scrubbing.
Skip abrasive pads. Scratches in plastic hold oil and pigment even more effectively than the smooth surface did, so scrubbing hard today makes tomorrow worse. The same principle governs nonstick cookware rules.
Step two: stains
Make a paste of baking soda and a little water, spread it over the stained area, and let it sit for a few hours or overnight. Baking soda is mildly alkaline and a very fine abrasive, so it lifts pigment without cutting the plastic.
Alternatively, fill the container with warm water and a tablespoon of baking soda and let it soak overnight.
Sunlight works too, and it is free. Wash the container, leave it damp, and set it outside or on a bright windowsill for several hours. Ultraviolet light breaks down many of the pigments that cause orange staining.
For heavier discoloration, an oxygen bleach powder dissolved in warm water per the label works well as an overnight soak. Ventilate, and never combine it with chlorine bleach or with any acid.
Source: cleaning chemistry references on surfactants and alkaline agents
Step three: odors
Odor usually means residual oil, so repeat the degreasing step first with hotter water and more soap.
If a smell survives that, fill the container with warm water and two tablespoons of baking soda, cap it, and leave it overnight. Rinse and air dry.
Crumpled newspaper sealed inside for a day or two absorbs stubborn odors. So does a handful of dry coffee grounds or a few tablespoons of dry rice, left sealed and then discarded.
A dilute white vinegar soak works on some odors, particularly dairy and fish. Rinse thoroughly afterward, and never mix vinegar with bleach or with hydrogen peroxide in the same container.
The lid is the real problem
Most container odor lives in the lid, not the base. Snap-on lids with a silicone gasket trap water and food in the channel underneath the seal, and that channel never dries.
Pull the gasket out. Nearly all of them come out with a fingernail or the tip of a butter knife, and there is usually a visible tab.
Wash the gasket separately with hot soapy water, and wash the groove it came from with a brush. Expect the groove to be genuinely dirty the first time.
Dry both completely before reassembling, and store lids with the gasket in place but the lid off the container so air circulates. A pressure cooker ring works the same way, as covered in a pressure cooker sealing ring.
Dishwasher rules and drying
Most food containers are dishwasher safe on the top rack only, where heat is lower. Bottom-rack heat warps thin plastic and distorts lids so they no longer seal.
Plastic also comes out of a dishwasher wet, because it does not hold heat the way glass and ceramic do. Towel dry it or leave it out to air dry rather than stacking it damp.
If containers come out of the dishwasher greasy or gritty, the machine is the problem rather than the plastic. Check the dishwasher filter and spray arms.
Store containers with lids off or loosely set on top. A sealed damp container develops a stale smell within days, and that is a problem the same shelf will keep producing. Storage discipline matters here for the same reasons it does in cleaning and rotating a pantry.
FAQ
How do I get tomato stains out of plastic containers?
Wash with hot soapy water first to remove the oil carrying the pigment, then either soak overnight in a baking soda solution or set the washed, still-damp container in direct sunlight for several hours. Sunlight breaks down the pigment and often clears it completely at no cost.
Why do my container lids smell even after washing?
Because the silicone gasket in the lid was not removed. Food and water get trapped in the channel underneath it and never dry out. Pull the gasket, wash it and the groove separately with hot soapy water, dry both fully, and the smell usually disappears.
Can food storage containers go in the dishwasher?
Most are dishwasher safe on the top rack, where temperatures are lower. Bottom-rack heat warps thin plastic and can distort lids so they stop sealing. Check the symbol on the bottom of the container, and hand wash anything unmarked.
Is a stained plastic container still safe to use?
Staining is cosmetic discoloration from pigment absorbed into the surface and is generally not a safety issue on its own. Replace containers that are cracked, deeply scratched, cloudy and brittle, or warped so they no longer seal, since damaged plastic holds residue and cannot be cleaned properly.
Does baking soda actually remove odors from plastic?
Yes, for many odors. Baking soda neutralizes acidic odor compounds and its mild alkalinity helps lift the residual oil that carries the smell. It works best as an overnight soak in solution rather than a quick scrub, and it works best after the container has already been thoroughly degreased.
Should I switch to glass containers?
Glass does not absorb oil, pigment, or odor, so it solves the staining and smell problems entirely. The tradeoffs are weight, breakability, and cost. A practical middle ground is glass for anything tomato-based, oily, or strongly spiced, and plastic for dry goods and lunches.
For the whole-home version of this work, see house cleaning services.
Kitchens accumulate a surprising amount of low-grade work like this, and it is usually what gets skipped when the week is busy. If you want the room handled on a regular schedule, 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.