Phlebitis (Superficial Venous Thrombosis): Symptoms, Causes & Treatment

If you’re here because you’ve noticed a painful, red, cord‑like vein or you’ve been told you have phlebitis or superficial venous thrombosis (SVT), you’re not alone. Many people want to understand whether this condition is serious, why it happens, and what they should do next. This page is written to help you understand what phlebitis is in clear terms so you can feel informed and reassured.

What is phlebitis?

Phlebitis means inflammation of a vein, usually one close to the surface of the skin.
When a small blood clot forms within that inflamed vein, it is known as superficial venous thrombosis or superficial thrombophlebitis.

Phlebitis most commonly affects veins in the legs and is frequently associated with varicose veins.

What causes phlebitis?

Phlebitis develops when blood flow within a vein becomes sluggish or turbulent, leading to irritation of the vein wall. Common causes and risk factors include:

• Varicose veins


• Prolonged immobility (long journeys, bed rest)


• Recent surgery or injury


• Pregnancy or the post‑partum period


• Hormone therapy or oral contraceptives


• A previous history of blood clots


• Active cancer or clotting disorders

Symptoms of phlebitis

People with phlebitis often notice:

• A tender, firm, cord‑like vein under the skin


• Redness or warmth over the affected area


• Localised swelling


• Aching or pain that worsens when standing or walking

Symptoms are usually confined to the area of the affected vein, which forms a hard, red and painful lump underneath the skin.

Is phlebitis dangerous?

In most cases, phlebitis is uncomfortable rather than dangerous. However, in some situations the clot can extend into the deeper veins of the leg. This is known as deep vein thrombosis (DVT), which carries a risk of pulmonary embolism.

For this reason, phlebitis should always be properly assessed, particularly when symptoms are severe, spreading, or located near the groin or behind the knee.

How is phlebitis diagnosed?

Diagnosis begins with a doctors appointment and through examination. An ultrasound scan is often recommended to confirm the presence of a clot, its length and to check whether the deeper veins are involved. Phlebitis is divided into two categories:

Low‑risk and higher‑risk phlebitis

Low‑risk phlebitis

Low‑risk phlebitis usually involves a short segment of vein, well away from the deep venous system,with mild symptoms and no significant risk factors.

Higher‑risk phlebitis

Phlebitis may be considered higher risk when the affected vein lies close to where superficial veins connect with the deeper venous system, or when a longer segment of vein is involved. In these situations, there is a greater chance that the clot could extend into the deeper veins.

Risk is also higher when symptoms are severe or worsening, or when there is a personal history of previous blood clots. Certain medical situations, such as pregnancy or active cancer, can further increase the likelihood of complications and influence how phlebitis is managed.

When phlebitis is considered higher risk, closer monitoring and additional treatment are recommended to reduce the chance of progression.

Treatment options for phlebitis

Supportive treatment

Many cases of phlebitis settle with simple supportive measures aimed at reducing inflammation and improving blood flow. Compression stockings are often recommended, as they help support the veins and reduce discomfort, particularly when standing or walking for long periods.

Anti‑inflammatory medication may be used to ease pain and swelling where appropriate, alongside warm compresses applied to the affected area. Keeping the leg elevated when resting can also help reduce swelling.

Staying mobile is important. Gentle walking encourages circulation and helps prevent blood from pooling in the veins, which can otherwise slow recovery.

Anticoagulation (blood‑thinning medication)

In higher‑risk cases, a short course of anticoagulation may be recommended to prevent clot extension.The choice of medication depends on individual factors and is carefully assessed.

Treating underlying varicose veins

Once the inflammation has settled, treating the underlying varicose veins varicose veins will prevent any further attacks from happening.

At The Vein Clinic, Swindon, we offer all leading treatments for underlying varicose veins, allowing us to tailor the approach that’s right for you. Options include endovenous laser therapy, ultrasound‑guided foam sclerotherapy, and Venclose™ radiofrequency vein closure. No other clinic in the region offers this full range of consultant‑delivered treatments, giving you access to the safest, most effective options available.

When should I seek urgent medical advice?

Urgent assessment is recommended if you experience:

• Sudden or increasing leg swelling


• New or worsening calf pain


• Shortness of breath


• Chest pain


• Coughing up blood

Preventing phlebitis in the future

After an episode of phlebitis, many people are keen to reduce the risk of it happening again. Maintaining regular movement and avoiding long periods of immobility can make a significant difference, particularly during travel or prolonged sitting.

Compression stockings may be advised in certain situations, especially for those with underlying vein problems. Maintaining a healthy weight and staying well hydrated also support good circulation.

For people with varicose veins, addressing the underlying vein condition can be one of the most effective ways to reduce the risk of recurrence. We can advise whether further treatment would be beneficial once the inflammation has settled.

A reassuring final word

Phlebitis can be painful and worrying, but with proper assessment and appropriate treatment,
most people recover fully. Understanding the condition helps you feel more confident and prepared when discussing your care.

If you are concerned about phlebitis or varicose veins, contact us to arrange a specialist assessment.