Hubbie's t-shirts...

[FaceDirectionOfTravel]

all end up with white 'wrinkle ' marks on the sides at the bottom within three months. They look awful. Like a deodorant mark but in a weird place. What is it? Can I prevent it?

If you are pegging them out by the bottom this can happen. Try pegging them under the arms.

Hang them on drying racks over the middle.

I'm no help at all, but every single one of dp's t-shirts has a grease stain down the front and mysterious little holes near to the bottom.

Mysterious little holes: I have tracked this down to my belt buckle.