Permanent press crease lines make a lasting impression in fabric because they are set using very high heat and a chemical treatment during the clothing manufacturing process. Permanent press creases are designed to withstand the temperatures of standard household washing machines and dryers. However, it is possible to remove these creases without ruining the fabric of your good pair of trousers or nice shirt.
Prepare a solution of white vinegar and water, using 2 or 3 tbsp of white vinegar for every cup of water. Make enough solution to submerge the garment for soaking.
Soak the permanent press garment and the cotton pressing cloth in the vinegar solution for at least 30 minutes.
Remove the garment and the pressing cloth from the solution. Squeeze out excess moisture.
Set your iron as hot as it will go and activate its steam setting. Lay the garment flat on an ironing board and place the pressing cloth over the permanent press crease line. Iron the pressing cloth over the crease lines, flattening them until they disappear.
Launder the permanent press garment and the pressing cloth in a normal wash to get rid of the vinegar smell.
Examine the permanent press garment after washing. Do not dry the garment if creases are still visible, because heat from the dryer may set the creases. If you still see crease lines, repeat the soaking and ironing process until they disappear.
Most dry cleaners and full-service laundromats have industrial machines that go to very high temperatures. If you are unable to remove permanent press crease lines yourself, take the garment to a professional.