THE BRONX - Hair coloring is a monthly routine for many women, but doctors say that a common chemical in dyes has been linked to severe allergic reactions.

It's called paraphenylenediamine, and doctors and hair stylists say women should always test a small amount of new dye before getting it fully applied.

The symptoms range from itching and hives to swelling and anaphylaxis -- which is a life-threatening allergic reaction that can put someone into shock or cause throat closure and suffocation.