What Causes A Red Rash Vertically Across The Navel?

I am a 32 years old female. Never had any medical problems except for I have found a vertical red line about 2 inches from my belly button on the left side. This would be my lower left side Of my stomach. It itches a little bit I thought it would disappear however it has been there for over a month and it seems as if it is getting a little longer everyday. Any help will be appreciated.