Just bought these cups from IKEA.
Beside from being dusty, I asked myself whether I should put these once before usage into the dishwasher to "wash away toxics" that might be on the surface of the cups.
On the other hand, this might be pure superstition.
My question:
Should I dishwash plastic cups/plates before first use?
Generally, yes, to wash off any chemicals that might have been used to finish the plastics or rinse any sprue away. If you're going to be putting the dishwasher on anyway, you might as well throw them in.
Lemon and or pine oil (lemon first) could be helpful along with baking soda mixed in, shake it around or use as a warm washing mix. Alternatively you can use soap and warm water, just be sure it smells like clean plastic when you're done, not chemicals from production or from your soap.
