I have a bulging vein on my forehead, it comes and goes. should i be concerned?

Forehead vein: What you are describing sounds like normal anatomical variation. Check with your doctor should you have any concerns.

Probably normal: This is very common, and is probably normal.

Forehead veins.: Forehead veins often change in size throughout the day due to many factors such as hydration, sun exposure, hereditary, heat, physical activity, stress and anything that would make the veins dilate or constrict. Forehead veins are normal. If the veins cosmetically concern you then they can be treated by sclerotherapy or surgical removal with excellent cosmetic results. See a vein specialist.