It is recommended you dont use it in the first trimester i think, but ive asked two drs and two chemists and they all said it was fine it is just preferred u wait till second trimester. I didnt leave the dye in for as long and didnt rub it into my scalp as much and had all the windows open (the guy next door copped an eyefull he was happy). I think just be sensible, dont over do it and read the instructions if u do want to use them and perhaps check with ur own dr if you are worried