Why Does My Baby's Silicone Cup Smell After Washing? Causes and Fixes

Quick answer

A lingering smell in your baby's silicone cup after washing is usually caused by food oils or residue trapped in the porous silicone surface. To fix it, wash with warm soapy water, then sanitize with a baking soda paste or vinegar solution. If the odor persists after deep cleaning, replace the cup—silicone can break down over time.

You wash your baby's silicone cup, but the smell of old formula or milk just won't go away. This is a common frustration for parents, and it's not a sign that you're doing anything wrong. Silicone is naturally porous at a microscopic level, which means it can trap oils and residues that regular dish soap may not fully remove.

The good news? Most of the time, you can eliminate the odor with a few simple steps. In this guide, we'll walk you through the likely causes, practical fixes, and how to know when your cup has reached the end of its useful life.

Why silicone cups hold onto smells

Silicone is a popular material for baby feeding products because it's soft, durable, and free of BPA. But it's not completely non-porous. Fatty foods like milk, formula, and purees can leave microscopic oil residue that builds up over time. When that residue oxidizes, it creates the sour, musty smell you notice after washing.

Another culprit? Incomplete drying. Water trapped inside the cup or in crevices can lead to mildew, which adds a different, musty odor. Hard water minerals can also react with silicone, making it look cloudy and smell stale.

• Always air-dry silicone cups upside down on a drying rack to prevent trapped moisture.



• Check for any soap residue—leftover dish soap can also cause a weird smell.

How to remove odors from silicone baby cups

Start with a simple hot water and dish soap soak. Use a bottle brush to scrub the inside and outside thoroughly, paying attention to any textured areas. Rinse well and let it dry completely before the next use.

If the smell persists, make a paste of baking soda and water, apply it to the cup's interior, and let it sit for 15–20 minutes before rinsing. You can also soak the cup in a 1:3 white vinegar and water solution for 30 minutes—just rinse it thoroughly afterward to avoid a vinegar taste.

One more option: place the cup in a bowl of warm water with a denture tablet. This can be surprisingly effective at lifting odors from silicone, and it's food-safe for baby gear.

• Never boil silicone in a plastic bag—steam or dishwasher-heated cycles are safer if you need high-temperature cleaning.
• Test any cleaning method on a small area first to avoid damaging the silicone.

What not to do when cleaning silicone cups

Avoid abrasive scrubbers or harsh chemical cleaners, as they can scratch the silicone surface, creating more places for odors to hide. Also, don't put silicone cups in the dishwasher on a hot cycle with a drying element—the high heat can degrade the material over time and make it more prone to absorbing odors.

If you use the dishwasher, choose a gentle cycle and remove the cup before the heated dry phase. Air drying is always the gentlest option.

• Skip bleach and ammonia-based cleaners—they're too harsh for baby feeding items.

When to replace the cup

Even with careful cleaning, silicone has a lifespan. If the smell doesn't go away after multiple deep-cleaning attempts, or if the silicone feels sticky, discolored, or has visible cracks, it's time to replace the cup. That's normal wear and tear, not a personal failure.

Regular replacement is also a good safety practice. Over time, silicone can lose its structural integrity, and a degraded cup is harder to clean and could harbor bacteria.

• Replace silicone cups every 6–12 months, or sooner if you notice any damage.

Diagnosis and fix at a glance

• Symptom: Silicone cup smells sour or musty after washing.
• Likely cause: Trapped food oils or residue from milk, formula, or purees in the porous silicone surface, or incomplete drying.
• Corrective action: Wash with warm soapy water, soak in baking soda paste or vinegar solution, then air-dry completely.
• Stop point: If the smell persists after multiple deep-clean attempts, or if the silicone shows signs of degradation (cracks, stickiness), replace the cup. Regular replacement keeps your baby's feeding gear safe and hygienic.

Feeding gear that's built with hygiene in mind

• Straw Replacements: The Straw Replacement Packs pair with the Mini Cup + Straw or Happy Cup + Straw. Straws are a prime spot for stubborn odors. Replacing them regularly keeps your baby's cup fresh and ensures the straw stays in good shape for cleaning.
• Straw Cleaner: ezpz’s Straw Cleaner assists with washing ezpz straws as well as pacifiers, nipples, water bottle lids, blenders and other mealtime gear. Using a dedicated straw cleaner helps you reach every crevice, preventing the trapped residue that causes lingering smells. It's a small, budget-friendly addition to your cleaning routine.
• Bottle Brush: The Bottle Brush was designed to clean bottles, water bottles, cups, and cookware. Due to the silicone material, the Bottle Brush is hypo-allergenic, odor-resistant, and long-lasting. A good bottle brush is essential for reaching the bottom of cups and bottles. Since this brush is also silicone, it won't scratch your cup's surface, keeping it smooth and easier to clean.

A smelly silicone cup doesn't mean you have to throw it away right away. Start with a thorough cleaning, try a baking soda or vinegar soak, and make sure it dries completely. If the odor sticks around after that, it's time to invest in a replacement. Keeping your baby's feeding gear fresh is part of good hygiene—and a clean cup makes mealtime more pleasant for everyone.