Certain beverages can harm the skin. Alcohol and coffee cause the tiny blood vessels to widen. These vessels are beneath the skin surface and result in us looking flushed and tired. Though this effect is initially temporary, excessive drinking may cause permanent widening of blood vessels. As a result they are apparently visible as thread veins. Other causes of thread veins are heredity, effects of the sun, spicy diet and extremes of temperature. Though heredity can't be modified you can certainly avoid the other factors to check the appearance of thread veins.