If you have a hair care product that contains this you might want to stop using it *right now*.
I recently attended a conference of neuroscience researchers at the University of Pittsburgh, one of whom has found that this compound (as well as its relative methylisothiazolinone, or MIT,) is a mammalian neurotoxin. When these results are properly published I will post the reference, and perhaps even some excerpts if I feel like violating copyright law.
There are many hair care products that do not use either of these compounds, though you may find that so-called "natural" or "botanical" products are not often MIT/MCI free.
(Of course, if you really believe that putting plant extracts in one's hair helps it get clean, then you might as well keep using your spontaneous-orgasm-in-a-bottle-with-papaya folicle treatment; I don't think the neurotoxicity will bother you much . . .)