The fastest way to clean moldy cups
Soak the cup in white vinegar for one to two hours, then scrub the inside with a bottle brush or old toothbrush. Rinse thoroughly under running water and dry completely before storing. For cups with stubborn mold or dark staining, repeat the soak or use a paste of baking soda and water instead of vinegar alone.
If the mold smell lingers after vinegar, fill the cup with hot water, add two tablespoons of baking soda, and let it sit overnight. The baking soda absorbs odors that vinegar leaves behind. Rinse and dry in sunlight if possible — UV light kills remaining spores and helps prevent regrowth.
For glasses with mold trapped under a stuck-on label or in a narrow rim, soak first to soften the mold, then use a thin brush, old electric toothbrush, or pipe cleaner to reach tight spots. Never use bleach on cups you drink from, even diluted — residue is hard to rinse completely and poses a health risk.
Key Takeaways
- White vinegar is the safest and most effective cleaner for drinking cups; soak for one to two hours, then scrub and rinse thoroughly.
- Baking soda paste works well for stubborn mold and also removes odors that vinegar cannot eliminate.
- Dry cups completely and store them upside down or in a well-ventilated space to prevent mold from returning.
- Avoid bleach on drinking vessels because it leaves toxic residue that is difficult to rinse away completely.
- If mold returns repeatedly, the cup may have a crack or porous glaze; replacing it is safer than repeated cleaning.
Why mold grows in cups and how to stop it
Mold grows in cups when moisture stays trapped inside — usually because the cup was put away damp, stored in a humid cabinet, or left sitting with liquid for days. The rim and the interior seam where the cup meets the base are the most common spots because water pools there and dries slowly.
To prevent mold, dry cups completely before storing them. Stand them upright on a clean dish rack or towel for at least 30 minutes after washing, or use a clean cloth to wipe the inside dry. Store them in a cabinet with good air circulation — avoid stacking damp cups or storing them in a closed, humid space like under a sink.
If you notice a cup smells musty or has a white or black film even after washing, it likely has a hairline crack or porous glaze that traps water inside the material itself. These cups are difficult to fully dry and will develop mold repeatedly. Replacing the cup is more practical than cleaning it over and over.
Vinegar versus baking soda: which works better
White vinegar kills mold spores and dissolves the film quickly. It works best on fresh mold or light staining. The acidity breaks down the mold structure, and the smell fades once the cup dries. Soak in undiluted white vinegar (5% acidity) for one to two hours, scrub, and rinse well.
Baking soda works slower but is better for stubborn, dark mold and for removing the musty smell that lingers after vinegar cleaning. Mix three parts baking soda to one part water to form a paste, explore it to the moldy area, let it sit for 15 to 30 minutes, then scrub and rinse. Baking soda is also gentler on delicate or decorated cups.
For the best result, use vinegar first to kill the mold, then baking soda to remove the smell and any remaining staining. If the cup still smells musty after both treatments, fill it with baking soda and water and let it sit overnight — the longer soak absorbs odors that a short scrub cannot reach.
Cleaning cups with narrow openings or stuck-on debris
Cups with narrow mouths, insulated walls, or decorative rims trap mold in places a regular sponge cannot reach. Soak the cup in vinegar first to soften the mold, then use a bottle brush, old toothbrush, or pipe cleaner to scrub inside. For very narrow spaces, a thin wooden skewer or chopstick wrapped in a cloth works to dislodge mold from seams.
If the cup has a stuck-on label or dried residue, soak it longer — 2 to 4 hours — so the vinegar softens both the mold and the debris. Once soft, scrub gently to avoid scratching the cup. For insulated cups with a gap between the inner and outer walls, mold can grow in that space where you cannot reach it; these cups are usually not worth cleaning and should be replaced.
An old electric toothbrush on a low setting can scrub stubborn mold faster than hand scrubbing, especially in textured or ridged cups. Wet the brush, dip it in baking soda paste, and let the vibration do the work. Rinse thoroughly afterward to remove all baking soda residue.
Drying and storing cups to prevent mold from returning
After cleaning, dry the cup completely before putting it away. Set it upright on a clean rack or cloth for at least 30 minutes, or wipe the inside with a clean, dry cloth. Pay special attention to the rim and the seam where the cup meets the base — these spots hold water longest and are where mold starts.
Store cups in a cabinet with air circulation. Avoid stacking them while damp or storing them in a closed, humid space. If your kitchen is very humid or your cabinet tends to trap moisture, leave the cabinet door cracked open or store cups in a different location. Some people keep drinking cups in a cupboard near a window or in a room with lower humidity.
If you live in a very humid climate or your cups develop mold frequently despite proper drying, consider storing them upside down. This prevents water from pooling inside the cup and allows air to circulate around the rim. Wipe the cup dry before flipping it over.
When to throw a cup away instead of cleaning it
If a cup develops mold repeatedly even after thorough cleaning and proper drying, it likely has a structural problem — a hairline crack, a chip, or a porous glaze that absorbs and traps water inside the material. These cups cannot be fully dried and will continue to grow mold.
Similarly, if the cup has a faint smell that does not go away after vinegar and baking soda treatment, or if you see mold growing inside the walls of an insulated cup, replacement is the practical choice. Spending time cleaning a cup that will mold again in a few weeks is not worth the effort.
Cups with decorative glazes or finishes that are flaking or peeling should also be discarded, because mold can hide under loose glaze and cleaning will not reach it. Your health is more important than saving a single cup.
Frequently Asked Questions
Can I use bleach to clean mold out of cups?
No. Bleach is toxic if swallowed, and even diluted bleach leaves residue that is difficult to rinse completely from porous cup material. Vinegar and baking soda are safer and work just as well. If you use bleach on a cup, rinse it at least five times with hot water and let it air dry for several hours before using it again.
How long does vinegar take to kill mold in a cup?
Vinegar begins killing mold spores within 15 to 30 minutes, but a full one- to two-hour soak ensures the mold is completely dead and the film is dissolved. For very stubborn mold, soak overnight. After soaking, scrub the cup to remove any remaining debris, then rinse thoroughly.
Why does my cup still smell musty after I clean it?
Vinegar kills mold but does not always remove the smell. Use baking soda paste or fill the cup with baking soda and water and let it sit overnight. Baking soda absorbs odors that vinegar leaves behind. If the smell persists after both treatments, the cup may have a crack or porous material that has absorbed the smell permanently.
Is it safe to drink from a cup that had mold?
Yes, if you clean it thoroughly with vinegar or baking soda and rinse well. Mold itself is not dangerous once it is dead and removed, but some mold species produce toxins. To be safe, soak the cup in vinegar for at least one hour, scrub it, and rinse multiple times before using it again.
Can I put a moldy cup in the dishwasher?
A dishwasher will not remove mold effectively because the water does not soak long enough and the heat alone does not kill all spores. Soak the cup in vinegar first to kill the mold, then run it through the dishwasher. For cups with stubborn mold, hand-scrub after soaking for best results.