What cause marks kn skin that looks like hickies?

Bruises: Ecchymoses or bruises of the skin are caused by damage to superficial blood vessels.

Hickies?: This is a tough one...Hickies can look bruised (broken blood vessels) or just red (inflamed skin). If they are bruise-like areas on your forearms, they are probably minor traumatic bruises--so minor you will not remember the trauma. See your doctor for the best answer.