Most dry cleaners use the toxic chemical perchloroethylene—also known as tetrachloroethylene—to clean clothes. Classified as a hazardous air contaminant by the EPA, perc can also contaminate drinking water when it gets into the water table and has been identified as cancer-causing by the International Agency for Research on Cancer, among other organizations.
Perc has also been linked to skin irritations, which is great to know when you break out in a gnarly rash after wearing your freshly-cleaned shirt.
Many fabrics can be hand-washed in cold water and air-dried rather than dry cleaned. If you have to go dry, look for “environmentally friendly” cleaners that use non-toxic soaps instead of chemicals to clean clothes; this process is sometimes known as “wet” or “steam” cleaning. Finally, if you can, opt out of the plastic bag—or at least bring it back to for the cleaner to recycle.