I often get an itchy chest, since I have been on finasteride. I have a moderate to large amount of hair on my chest, and I never connected the two, but now I see there is a connection... sometimes I itch it so much it bleeds.
It tends to come and go... moisterizing it with lotion seems to help. If you use nizoral or another dandruff shampoo, try using the excess on your chest, it might help... it usually does for me...