the only thing likely to cause distortion of plastic i think is high heat.
a 60 degree wash might bother them a bit, but i doubt simply wearing them will fail to fix em.
if in doubt do a cold or a 30 deg wash.... but rinse the buggers out twice over or they might end up honking worse than ever!
having said all of the above...i am a mucky bugger! so what the hell would i know?!