I am a pre-washer. Just this week my husband got new work uniforms (he works as a fitter/welder in the automotive trade). Washed them all (and cut and hemmed the pants). After day three he had a massive allergic reaction, everywhere the fabric touched he had swelling, welts, heat and itching. As the dye didn't run I guessed it was formaldehyde. Soaked them in boiling water, rinsed, soaked in milk and cold water for 2 hours, rinsed in cold water and then washed as usual with a vinegar rinse. The problem seems to be solved.
This is the first time he has been allergic to anything, and he is as tough as old boots (the kids call him "The Machine"). So even pre-washing, for some things isn't enough.