I heard its mainly the fumes that can be harmful, just make sure they know your pregnant and its well ventilated.
I was told just not in the first trimester by my hair salon and my doc! After that its fine.. just make sure theirs air.
It's fine, just know sometimes your hair can come out darker then normal! The hormones are crazy and for some reason mine and 4 girlfriends hair came out a shade darker.
It's fine they say after 12 weeks ur okay