Contrary to popular belief parabens do not hurt your hair at all (let me qualify this statement buy saying that some women do find them too harsh for their hair, but it does not block moisture like mineral oil or petroleum and it does not build up silk silicone). In fact they are used as a preservative in cosmetic products. However, the general fuss over not using parabens is internal.
A UK study (conclusions published in the early 2000s) found high concentrations of parabens in breast tumors. Parabens have been found to mimick the hormone estrogen when released into the bloodstream; this can cause abnormal cell growth, cancer, hormonal disruption, etc. Let it be known that this study states that LARGE doses created this result. However, this study does not say that parabens CAUSED the tumors, but instead they go on to say that deodorants (which all contain parabens) and are used underarms are directly related to causing cancer. The American Cancer Society was quick to put out a statement saying that they disagree with the conclusions of this study, but further research needs to be done on the subject of parabens.
On the flip side a 2009 European study shows that propylparaben and butylparaben (two most common cosmetic parabens) are not entering the blood stream through cosmetic products. They found that the parabens were only partially absorbed and metabolized before entering the blood stream. Thus no traces of parabens were found in the blood stream.
There is so much more info, so take a look around google and see what you can see.
Please be an informed user or nay sayer of parabens, not an uninformed fanatic. I completely understand the studies done with parabens and I choose to continue to use them. Eating parabens worries me more than topically applying them to my hair. I choose to be an informed unconcerned user of parabens.