Never Just Rinse Your Thermos with Water! Experts Reveal 2 Proper Cleaning Methods to Avoid Ingesting Bacteria

Many people routinely carry reusable water bottles or eco-friendly cups, but often believe that since they only fill them with plain water, special cleaning isn't necessary—rinsing briefly before reuse is common practice. In reality, areas like the mouthpiece, lid, straw, and silicone ring are hotspots for bacteria and grime buildup. If not thoroughly cleaned over time, these areas can develop unpleasant odors and even pose health risks.

Just how dirty can a thermos get? A foreign study on reusable water bottles found that if not cleaned for several consecutive days, biofilms—colonies of bacteria—can form on the rim, straw, and lid. The bacterial count in these areas may exceed that of many everyday objects we frequently touch.

Dr. Chen Chongxian, a family medicine physician, warned on Facebook that both plastic bottles and stainless steel thermoses can develop biofilms if the interior remains moist for extended periods. Since drinking water isn’t completely sterile and our mouths touch the bottle mouth every time we drink, bacteria continuously adhere to the inner surfaces. In children’s bottles, food residue increases the risk, providing nutrients that accelerate bacterial growth. If pathogenic bacteria are present, long-term exposure could harm health.

Tan Dunci, known as the 'Mother of Non-Toxic Living,' emphasized on the show 'Wishing You Health' that while using eco-cups is environmentally responsible, skipping proper cleaning is dangerous. She noted that if the inside feels slimy, a biofilm has already formed and must be scrubbed immediately with a brush. The silicone ring, which traps moisture and debris, must be removed and cleaned thoroughly, as crevices are ideal breeding grounds for bacteria and mold.

Tan recommends disassembling the bottle, lid, and all components for separate cleaning each time. Use small brushes and detergent for tight spaces. If the silicone ring is hard to reattach, dry it first, then chill in the refrigerator—this makes it slightly firmer and easier to install. Always ensure the bottle is completely dry before reassembling. For bottles with ceramic or non-stick linings, use soft-bristle brushes to avoid scratching the surface and shortening the product’s lifespan.

Sources: 'Family Medicine/Occupational Medicine – Dr. Chen Chongxian,' 'Wishing You Health' Editor: Cai Huixin