There is always a risk when it comes to dying your hair. Some people do react to the chemicals within the dye and when that happens it can have some pretty horrid results. Your face could swell, your hair could fall out and your eyes could become incredibly sore too. However, generally most people are fine.
On the actual hair dye packaging or in the leaflet enclosed, you should see that on the directions it tells you to do a small test first. This is basically where you put a tiny bit of the colour on a small patch of your hair. Many people prefer to put it near their ear under their hair so that it does not show up very much. If no problems occur in the amount of time that it tells you to leave it on, you should be fine. However there is still a chance that things could go wrong so always be prepared for that and know the risks when you are colouring your hair.
On the actual hair dye packaging or in the leaflet enclosed, you should see that on the directions it tells you to do a small test first. This is basically where you put a tiny bit of the colour on a small patch of your hair. Many people prefer to put it near their ear under their hair so that it does not show up very much. If no problems occur in the amount of time that it tells you to leave it on, you should be fine. However there is still a chance that things could go wrong so always be prepared for that and know the risks when you are colouring your hair.