Sunlight is the real stain killer

The most effective way to get tomato and curry stains out of plastic lunch boxes is a paste of baking soda and dish soap, followed by a few hours in direct sunlight.

Curry stains are turmeric, and turmeric is an oil-soluble dye. That’s why water alone does almost nothing. Dish soap cuts the oil and lifts the pigment, while baking soda gives you just enough gentle abrasion to work it out of the plastic’s micro-scratches without adding new ones.

The sunlight part is the secret weapon. UV light literally breaks down the pigment molecules. I’ve had boxes with old yellow curry stains look brand new after a couple hours on a sunny windowsill. If it’s winter or cloudy, the paste alone will get most of it — just let it sit on the stain for 10–15 minutes before scrubbing.

Two things to avoid: bleach, which can discolor or warp plastic, and anything scouring-pad rough. Scratches don’t clean better; they just give the next stain more places to hide.

The sun has been bleaching things for billions of years. Might as well put it to work.