Why Do Plastic Containers Turn Dull and Scratched Over Time?

The main reason plastic storage containers turn dull and scratched over time is repeated exposure to high heat in the dishwasher. The hot water and drying cycle slowly breaks down the molecular structure on the plastic's surface; a surface that started out smooth fills with microscopic cracks that scatter light and give it a dull look. The abrasive ingredients in dishwasher tablets and rinse aids also play a part. Every wash wears away a thin layer of the plastic's surface; that wear isn't noticeable after one wash, but it builds up over months until the container loses its original shine. Why do scratches form so easily? Scraping food out with a metal spoon or fork leaves fine scratches in the plastic's soft surface very easily. Those scratches don't just ruin the look — they also create tiny grooves where food residue and odors can settle in. Scrubbing with the rough side of a sponge leaves similar fine scratches; if you want a container to stay glossy longer, the soft side of the sponge is the better choice. What can be done to make containers last longer? Washing plastic containers in a spot in the dishwasher that's away from the bottom heating element slows down the dulling. Washing them by hand in warm water with a soft sponge, when possible, protects the surface the longest. Scraping off food residue with a spoon first instead of digging into the plastic, and using a wooden or silicone spatula, also goes a long way toward preventing scratches. Does microwaving also speed up the dulling? Repeatedly microwaving a plastic container wears down its surface much like the dishwasher does; hot, oily food in particular contributes to the plastic softening and developing microscopic roughness. Containers not labeled microwave-safe shouldn't be heated in one at all. Letting oily, spicy food sit in a container for a long time can also change the surface's chemical structure over time, not just stain it; these foods are better stored in glass when possible, leaving plastic containers for water-based, oil-free food. The number under the recycling symbol on a container shows the type of plastic; number 5, polypropylene, is usually one of the more heat-resistant types, but whether a container is microwave- and dishwasher-safe depends on its own label and the manufacturer's instructions, not the number. Plastic containers that regularly store pigmented food, like tomato sauce, can pick up a faint orange tint over time; this discoloration is a separate process from dulling and can usually be reduced somewhat with sun exposure or a baking soda paste. Old, heavily used containers can also start holding onto a faint smell over time; at that point, a sensible solution is retiring the container from food storage and using it just for dry goods instead. A container's lid usually wears out before the body does; for models that sell replacement lids separately, buying just a new lid can be a more economical fix than replacing the whole container. Placing the container right-side up in the dishwasher rather than upside down also keeps water from pooling inside and slows the dulling a bit.