Must wash first.
The garments that we buy from shops are either pre-washed, or
not.
Even it is pre-washed, after washing in laundry factroy, it will be
transported back to garment manufacturer, they will punch the metal
buttons(this process maybe done before or after wash), iron the
garments, then pack it in plastic bags, then put in boxes, then
ship out.
So before it is packed and after it is washed, it will be still
touched by the workers during transportion between laundry factroy
and garment manufacturer, and those who iron them, and those who
pack them.
So, if it's NOT pre-washed...... Even more hands have touched it
before you wear it.
