Spider veins don’t have an exact known cause. The condition may be a result of genetics, environment, or a combination of both. Certain people are also more at risk than others.

Telangiectasia is a condition in which widened venules (tiny blood vessels) cause threadlike red lines or patterns on the skin. These patterns, or telangiectases, form gradually and often in clusters. They’re sometimes known as “spider veins” because of their fine and weblike appearance.

Telangiectases are common in areas that are easily seen (such as the lips, nose, eyes, fingers, and cheeks). They can cause discomfort, and some people find them unattractive. Many people choose to have them removed. Removal is done by causing damage to the vessel and forcing it to collapse or scar. This reduces the appearance of the red marks or patterns on the skin.

While telangiectases are usually benign, they can be a sign of serious illness. For example, hereditary hemorrhagic telangiectasia (HHT) is a rare genetic condition that causes telangiectases that can be life-threatening. Instead of forming on the skin, telangiectases caused by HHT appear in vital organs, such as the liver. They may burst, causing massive bleeding (hemorrhages).

Telangiectases can be uncomfortable. They are generally not life-threatening, but some people may not like how they look. They develop gradually, but can be worsened by health and beauty products that cause skin irritation, such as abrasive soaps and sponges.

Symptoms include:

  • pain (related to pressure on venules)
  • itching
  • threadlike red marks or patterns on the skin

The symptoms of HHT include:

  • frequent nosebleeds
  • red or dark black blood in stools
  • shortness of breath
  • seizures
  • small strokes
  • port-wine stain birthmark

The exact cause of telangiectasia is unknown. Researchers believe several causes may contribute to the development of telangiectases. These causes may be genetic, environmental, or a combination of both. It’s believed that most cases of telangiectasia are caused by chronic exposure to the sun or extreme temperatures. This is because they usually appear on the body where skin is often exposed to sunlight and air.

Other possible causes include:

  • alcoholism: can affect the flow of blood in vessels and can cause liver disease
  • pregnancy: often applies large amounts of pressure on venules
  • aging: aging blood vessels can begin to weaken
  • rosacea: enlarges venules in the face, creating a flushed appearance in cheeks and nose
  • habitual corticosteroid use: thins and weakens the skin
  • scleroderma: hardens and contracts the skin
  • dermatomyositis: inflames skin and underlying muscle tissue
  • systemic lupus erythematosus: can increase skin sensitivity to sunlight and extreme temperatures

The causes of hereditary hemorrhagic telangiectasia are genetic. People with HHT inherit the disease from at least one parent. Five genes are suspected to cause HHT, and three are known. People with HHT receive either one normal gene and one mutated gene or two mutated genes (it only takes one mutated gene to cause HHT).

Telangiectasia is a common skin disorder, even among healthy people. However, certain people are more at risk of developing telangiectases than others. This includes those who:

  • work outdoors
  • sit or stand all day
  • misuse alcohol
  • are pregnant
  • are older or elderly (telangiectases are more likely to form as skin ages)
  • have rosacea, scleroderma, dermatomyositis, or systemic lupus erythematosus (SLE)
  • use corticosteroids

Doctors may rely on the clinical signs of the disease. Telangiectasia is easily visible from the threadlike red lines or patterns it creates on the skin. In some cases, doctors may want to make sure that there is no underlying disorder. Diseases associated with telangiectasia include:

  • HHT (also called Osler-Weber-Rendu syndrome): an inherited disorder of the blood vessels in skin and internal organs that can cause excessive bleeding
  • Sturge-Weber disease: a rare disorder that causes a port-wine stain birthmark and nervous system problems
  • spider angiomas: an abnormal collection of blood vessels near the surface of the skin
  • xeroderma pigmentosum: a rare condition in which the skin and eyes are extremely sensitive to ultraviolet light

HHT may cause the formation of abnormal blood vessels called arteriovenous malformations (AVMs). These may occur in several areas of the body. These AVMs allow direct connection between arteries and veins without intervening capillaries. This may result in hemorrhage (severe bleeding). This bleeding can be deadly if it occurs in the brain, liver, or lungs.

To diagnose HHT, doctors may perform an MRI or a CT scan to look for bleeding or abnormalities inside the body.

Treatment focuses on improving the appearance of the skin. Different methods include:

  • laser therapy: laser targets the widened vessel and seals it (this usually involves little pain and has a short recovery period)
  • surgery: widened vessels can be removed (this can be very painful and may lead to a long recovery)
  • sclerotherapy: focuses on causing damage to the inner lining of the blood vessel by injecting it with a chemical solution that causes a blood clot that collapses, thickens, or scars the venule (there’s usually no recovery needed, although there may be some temporary exercise restrictions)

Treatment for HHT may include:

  • embolization to block or close a blood vessel
  • laser therapy to stop bleeding
  • surgery

Treatment can improve the appearance of the skin. Those who have treatment can expect to lead a normal life after recovery. Depending on the parts of the body where the AVMs are located, people with HHT can also have a normal lifespan.