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The t-shirt in question is a pretty decent make: free spirit, wasn't exactly cheap, although it wasn't particularly expensive. Says 40 degree wash, not sure but I might have washed it at 30, but definitely not more than 40. Says iron with 2 dots, but i didn't bother ironing it. It says not to dry clean, bleach or tumble dry, which I didn't. The text says "wash inside out, wash deep colours separately, reshape whilst damp & hang to dry", all of which i think i followed: once the wash cycle finished it was hung on a normal clothes hanger till dry. Label also says its made from 100% cotton. I used just a supermarket own brand non-biological washing tablets: two in a full load.
The only thing i didn't follow was the ironing, which i didn't bother with (don't mind a few creases ;-) ), could that have caused it? I've now washed it 2 or 3 times and maybe worn it 3 or 4 times (had a clean clothes emergency the week before, in my defence it was only worn for a couple of hours each time). i wore it on saturday and i asked someone how old they thought the t-shirt was: they said 3 years!
i might take it back, but this has happened to me a few times so i'm thinking that it might be something to do with how i wear clothes because i'm sure i treat them correctly.
Thanks for the responses so far!