If they're stretching the right way, there should be no open wounds and stretching with acrylic should not be a problem.
However some people can be allergic to it, you could have torn it in your sleep by accidentally tugging on it, or perhaps you just weren't quite ready to stretch. Though I'm willing to bet it's the middle one ^^
My favourite pair of jewellery is actually a pair of 10g white acrylic spirals. Too bad I can't wear them anymore, although I guess I could always buy another pair for 2g
There seems to be a lot of stigma behind acrylic, but seriously there is nothing wrong with it as long as you're not destroying your ears by going up 3 sizes in one week, and as long as it's a GOOD QUALITY coated acrylic (it should be shiny) and not something cheap from china.
People seem to forget that the quality of the item your purchasing, even if it's steel or titanium, will have an affect since cheaper item= cheaper build materials and quality.
~Strick