Suggest Treatment For Red Blotches On Neck And Chest

My 24 yr old daughter gets red blotches on her neck and chest. Sometimes when she's nervous, and sometimes for no reason at all. They come and go. No itching, no welts or raised areas, no chicken-skin appearance. This has been going on for years. Her 3 sisters also have the same problem in vaarying degrees. I do not. She finds it very embarassing. Any advice?