Visible veins usually do not mean that something is wrong. They can be more noticeable because of:
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Naturally thin or fair skin
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Lower body-fat levels
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Aging, as skin becomes thinner
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Exercise or increased blood flow
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Heat, which causes blood vessels to widen
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Genetics
However, a new, prominent vein accompanied by swelling, pain, redness, warmth, or a hard/tender area deserves medical attention, particularly if it occurs in one arm or leg.
A sudden visible vein by itself is not a reliable sign of a particular disease or health condition.
