I keep getting red lines and bumps on my neck. what could cause this? hydrocortisone cream helps but it comes back.

Probably: This is probably a contact dermatitis. You are probably allergic to something. Please see your dermatologist for evaluation and to discuss treatment options. You probably will need patch testing.

Dermatitis?: I agree with Dr. Jackson. But the best way to identify this with any certainty is to have it medically evaluated.

Red lines,bumps: If these are very itchy and are at areas of pressure from clothing, rubbing,etc you could be dealing with dermatographism which is a state of skin reactivity related to hives. Otherwise simple contact dermatitis may be the problem.An allergist could evaluate,advise and treat you.