Some injuries can cause blood vessels in the back of the eye to bleed.

High insulin levels are known to cause blood vessels to become inflamed.

This causes the blood vessels to expand and the face to flush.

These drugs block an enzyme needed to form a substance that causes blood vessels to narrow.

These block the action of a hormone that causes blood vessels to narrow.

They help to clear nasal passages by causing blood vessels in the lining of the nose to narrow.

Prolonged use can cause blood vessels to be dilated for an extended period of time.

Secondhand smoke contains nicotine, which causes blood vessels in the brain to narrow.

In time, ongoing dilation may cause blood vessels to get larger and look like small red lines on the skin.

For some people, the lack of oxygen at high altitudes can cause blood vessels to constrict.