I have to disagree with the esteemed Mr. Kabbaz on this point. Washing a shirt after every wearing strikes me as unnecessary and wasteful. True, a quality shirt may last 50-100 washings, but why shorten the life of the shirt by washing it so frequently? As far as I'm concerned, the only appropriate answer to the question "when should I wash my shirt?" is "when it is dirty." I always was the shirt at the first sign of visible dirt, however, since I don't really perspire and am not susceptible to the dreaded "ring around the collar", this is often two, three, or more wearings. Even then, the only part of the shirt that shows any dirt is often the cuffs, so I will simply hand wash the cuffs.