Sclerotherapy for the treatment of varicose veins: what it involves, indications and results

What is sclerotherapy?

Sclerotherapy is a treatment used to close dilated veins that are visible under the skin or that are not functioning properly.

The procedure involves injecting a substance called a sclerosing agent directly into the vein; this can be administered in liquid or foam form. This substance triggers a controlled reaction in the inner wall of the vein, causing the walls to draw together and stick to one another.

The aim is to stop the vein from carrying blood. When the treatment successfully closes the vein, blood flow is naturally redirected to other vessels that are functioning properly. Consequently, blood does not become trapped in the leg.

Over time, the body gradually transforms and reduces the treated vein, which may become less visible or even disappear. However, closure is not always complete or permanent. Some veins require more than one session and, in certain cases, may reopen over time.

Sclerotherapy may be performed for medical, cosmetic or both purposes. It is used to treat small spider veins, reticular veins and certain varicose branches that may cause pain, heaviness, swelling or other discomfort associated with venous insufficiency. Clinical guidelines recommend the use of liquid or foam sclerotherapy in selected patients, depending on the type of vein and its characteristics.

From a medical perspective, it is considered a chemical ablation technique, as it aims to close the vein using a substance rather than heat. However, the common and more understandable term is sclerotherapy.

Liquid sclerotherapy and foam sclerotherapy

The medication can be administered in liquid form or as a foam. The choice depends, above all, on the size, depth and course of the vein.

Liquid sclerotherapy

The liquid form is mainly used for spider veins, reticular veins and other small vessels close to the skin. The specialist inserts a very fine needle and injects a small amount of the product. Several veins can be treated in a single session, although the extent of treatment depends on the maximum dose that can be used safely.

Foam sclerotherapy

The foam is prepared by mixing the medication with a gas using a controlled technique. Upon entering the vein, it temporarily displaces some of the blood, allowing the solution to remain in contact with the vessel wall for longer.

It is usually used on larger veins, varicose branches, varicose veins that have reappeared after other treatments, and certain venous segments that are difficult to access with a catheter. The foam is not simply a ‘stronger’ version of the liquid. It is a different formulation, with specific indications, dosages and precautions.

When is Doppler ultrasound used?

Venous Doppler ultrasound is used when the vein cannot be clearly seen or felt, when it lies deeper, or when it is necessary to determine its connection to other veins.

In medical terminology, the terms ‘duplex ultrasound’, ‘Doppler ultrasound’ or ‘ultrasound-guided sclerotherapy’ may also be used. In this factsheet, the term ‘Doppler ultrasound’ is primarily used because it is the most recognisable term for a member of the public without medical training in Spain.

The image allows the vein to be located, the position of the needle to be checked and the initial distribution of the foam to be observed. It also helps to determine whether there is abnormal backward flow of blood, known as venous reflux, in a main vein.

Current guidelines recommend the use of ultrasound guidance when treating deep varicose branches, perforating veins, recurrent varicose veins and venous trunks such as the saphenous veins.

In which cases might it be recommended?

Sclerotherapy may be appropriate when the veins to be treated are of a size, depth and course compatible with the technique.

For spider veins and very small veins, the aim is usually to improve the appearance of the skin, although some people also experience itching, stinging or local discomfort.

For larger varicose branches, the aim may be to achieve both cosmetic and functional improvement. The technique can reduce pain, swelling or a feeling of heaviness when these symptoms are related to the treated veins.

It is also frequently used to treat varicose veins that remain visible after thermal ablation or surgery, as well as certain cases of recurrence.

Ultrasound-guided foam sclerotherapy can be used on deeper veins and, in selected cases, on a saphenous vein. However, where there is significant reflux along a main vein, clinicians usually consider thermal ablation first, provided the anatomy allows it.

The choice does not depend solely on how large or conspicuous the varicose vein appears. Two veins that look similar may have different origins and require different treatments.

How do you know if it is the right treatment?

The assessment begins with an examination of the legs and a discussion of symptoms, previous treatments and personal medical history.

For small superficial veins, a detailed examination may be sufficient. Where there are larger varicose veins, swelling, skin changes, persistent pain or a history of previous procedures, it is usually necessary to supplement the assessment with a Doppler ultrasound scan.

This test allows us to check whether the venous valves are functioning correctly, identify the source of the varicose veins and examine the deep venous system.

A patient’s history of thrombosis, mobility, allergies and any medication that may affect the risk of bleeding or clotting is also reviewed.

Sclerotherapy may be a suitable option for one vein but not for another located very close by. For this reason, the decision to proceed must be based on each person’s individual venous pattern, not solely on the external appearance of the leg.

When might it not be recommended?

Sclerotherapy is not routinely carried out during pregnancy and is usually postponed until after childbirth. Nor should it be carried out if there is an active infection in the area, a known allergy to the product or acute venous thrombosis.

People with a history of thrombosis, severely reduced mobility, a high risk of blood clots or certain cardiopulmonary conditions require particularly careful assessment. Some of these circumstances preclude treatment; others necessitate modifying the technique, reducing the dose or putting in place additional preventive and monitoring measures.

Preparation before the session

Preparation is usually straightforward and the treatment is carried out on an outpatient basis. Before starting, the patient’s allergies, medication and history of thrombosis or bleeding are reviewed. Anticoagulants and antiplatelet agents must not be discontinued without medical advice.

General anaesthesia is not usually required, nor is it necessary to fast beforehand. The needle is very fine, although the injection may cause a stinging sensation or a brief feeling of pressure. On the day of treatment, it is usually recommended that you wear comfortable clothing and avoid applying creams or oils to your leg. The team will advise you if you need to wear a compression stocking.

How is it carried out?

The patient lies down whilst the specialist identifies the veins to be treated and cleans the skin with an antiseptic solution.

– Direct injection

When the veins are small and visible, the injection can be administered directly. The medication is injected slowly using a very fine needle.

– Ultrasound-guided injection

When the vein is deeper, the specialist uses ultrasound to position the needle precisely. If foam is used, they can see how it fills the selected segment.

During the injection, you may experience itching, pressure or a brief burning sensation. Any severe pain, difficulty breathing, visual disturbances or unexpected symptoms must be reported immediately.

– After the injection

Once the procedure is complete, a small pressure dressing may be applied to the treated areas and, depending on the case, a compression stocking or a bandage may be fitted. The patient can usually get up and walk around shortly afterwards. For some veins, it may be necessary to repeat the injection in a further session.

NICE (National Institute for Health and Care Excellence, UK) states that the available evidence supports the routine use of ultrasound-guided foam sclerotherapy, provided that appropriate patient selection, informed consent and monitoring for potential adverse effects are carried out.

Is it painful?

Most people tolerate sclerotherapy well. The injection is usually only slightly painful. As the solution is injected, you may feel a stinging sensation, warmth or pressure for a few seconds.

Afterwards, the vein may feel tender or hardened. In larger veins, this sensation may persist for several weeks whilst the closure process is completed. Severe pain, marked swelling or progressive worsening should not be considered a normal reaction and require medical assessment.

How many sessions are needed?

It is not always possible to complete the treatment in a single visit. The number of sessions depends on the number and size of the veins, the response to the medication and the maximum dose that can be safely administered.

Extensive spider veins may require several sessions even if each vessel is small. Larger veins may also need further injections if they do not close completely.

A period of time is allowed between sessions to allow inflammation, bruising and discolouration to subside. For this reason, the overall result on one leg cannot always be assessed immediately after the first treatment.

What results can be expected?

Sclerotherapy aims to close off the vein so that it no longer carries blood. Small veins usually fade gradually over the following weeks. Some disappear almost completely; others diminish but remain visible.

Larger veins may harden and feel like a cord before gradually shrinking. This process can take weeks or months. Improvement in pain, heaviness or swelling depends on whether these symptoms are actually related to the treated veins. If there are other insufficient veins or non-venous causes, the response may be partial.

Foam sclerotherapy can produce good results in varicose branches and recurrent veins. However, when used on a saphenous vein, there may be a higher likelihood of reopening or of requiring further sessions than with some thermal techniques. This difference does not make one option universally better: it necessitates choosing the treatment based on the anatomy and the clinical objective.

Risks and side effects

Most side effects are mild and temporary. It is common to experience minor bruising, itching, tenderness or redness around the injection sites.

A brown discolouration may also appear along the course of the vein. This hyperpigmentation usually fades, although it may persist for months and, in some cases, remain. Small reddish vessels sometimes appear around the treated area. This phenomenon is known as ‘matting’ or the formation of new small superficial veins.

In larger veins, blood may become trapped within the closed vessel. This is felt as a hard, dark or painful area and, in certain cases, can be drained via a small puncture. The vein may also become inflamed, leading to superficial phlebitis. Although this usually affects only a limited segment, close monitoring is required if the pain or redness spreads.

Deep vein thrombosis and pulmonary embolism are rare but serious complications. The risk depends on personal medical history, the extent of the treatment and other clinical factors.

Risks specific to the foam

Foam may cause some transient effects that are not common with the liquid formulation. These include blurred vision, flashes of light, headache, coughing or a brief sensation of tightness in the chest.

NICE states that these symptoms and other rare but relevant complications, such as neurological or cardiac events, should be explained during the informed consent process. Most transient symptoms resolve, but any persistent visual disturbances, difficulty speaking, loss of strength, chest pain or shortness of breath requires immediate assessment.

What is the recovery like?

Sclerotherapy usually allows patients to walk and engage in moderate activity from the very same day in most cases. Bed rest is not usually necessary. Walking promotes blood flow through the deep veins and prevents prolonged periods of immobility.

During the first few days, you may experience tenderness, tightness or small hardened areas.

– Compression stockings

The team may recommend a compression stocking or bandage after the session. The duration of use depends on the size of the veins, the type of product used and the clinical protocol.

– Work and exercise

Many people can continue with light activities. Returning to work depends on any discomfort and the physical demands of the job. Walking is usually advisable. Intense exercise, high-impact sports, saunas and very hot baths may need to be temporarily restricted. It is also advisable to protect areas with bruising or pigmentation from the sun, as exposure can darken the marks.

– Follow-up

A follow-up examination allows the specialist to check whether the vein has closed and whether the local reaction is progressing as expected. In small veins, the result is assessed once the bruising and swelling have subsided. In deeper veins, a Doppler ultrasound scan may be carried out.

If blood becomes trapped inside a closed vein, the specialist may drain it to relieve discomfort and reduce the risk of pigmentation. They may also schedule a further session if any segments remain open or if there are other veins that still require treatment. The subsequent appearance of new varicose veins does not necessarily mean that the procedure was performed incorrectly. Venous disease can progress and affect other veins over time.

Differences from thermal ablation

Sclerotherapy closes off the vein using a sclerosing agent. Thermal ablation uses a catheter that applies heat via laser or radiofrequency. Sclerotherapy is particularly useful for spider veins, tortuous branches, residual veins and certain recurrences.

Thermal ablation is frequently used when there is reflux along a saphenous vein and its course allows a catheter to be inserted. NICE sets out a sequence whereby, for certain varicose veins with trunk reflux, thermal ablation is offered first where appropriate; if this cannot be performed, ultrasound-guided foam sclerotherapy is considered, followed by surgery.

The two techniques can complement one another. For example, thermal ablation may close the main vein, whilst sclerotherapy can then treat any branches that remain visible or symptomatic.

Situations requiring special consideration

Sclerotherapy is usually postponed during pregnancy. Many varicose veins change after childbirth and can be reassessed once circulation has stabilised. A history of thrombosis does not automatically rule out treatment, but it does necessitate a thorough assessment of the venous system and individual risk.

People taking anticoagulants or antiplatelet agents should not alter their medication without medical supervision. Those with severely reduced mobility, known allergies, significant arterial disease or certain cardiopulmonary conditions also require careful assessment.

When to seek advice after treatment

Minor bruising, mild itching, tenderness and localised hardening may be part of the normal healing process. These symptoms should gradually improve.

You should contact the team if the pain increases, the redness spreads, a fever develops or the leg swells more than expected.

Seek urgent medical attention if you experience:

• Sudden difficulty breathing.

• Chest pain.

• Coughing up blood.

• Sudden and severe swelling of a leg.

• Loss of strength or sensation.

• Difficulty speaking.

• Persistent visual disturbances.

• Swelling of the face, lips or throat.

• Fainting.

The list is included as it allows for the rapid identification of situations that may require immediate attention.

Which specialists are involved

The assessment is usually led by a specialist in Angiology and Vascular Surgery, who investigates the cause and extent of the venous disease and determines which treatment may be most appropriate in each case.

At our hospital, we have a Varicose Vein Unit, which forms part of the Department of Angiology and Vascular Surgery and specialises in the diagnosis and treatment of varicose veins and other venous diseases. The assessment relies primarily on clinical examination and vascular Doppler ultrasound, which provide insight into the anatomy and function of the venous system before a treatment decision is made.

Where indicated, the Unit offers various treatment options, including minimally invasive techniques such as thermal ablation, microfoam and, in certain cases, treatment using high-intensity focused ultrasound. The choice of treatment is made on a case-by-case basis, depending on the characteristics of the affected veins and the individual’s clinical condition.

The nursing staff are also involved in preparation, post-treatment care and providing the necessary guidance throughout the care process.

Frequently Asked Questions

Is sclerotherapy effective for all varicose veins?

No. It is particularly useful for spider veins, varicose veins, residual veins and some recurrences. Certain saphenous veins may require thermal ablation or another technique.

Is it the same as chemical ablation?

Yes. Sclerotherapy is a form of chemical ablation, although ‘sclerotherapy’ is the most commonly used clinical and lay term.

Does the vein disappear once the session is over?

No. The medicine sets a gradual process in motion. It may take weeks or months for the vein to shrink.

Can it leave stains?

Yes. Brown pigmentation may appear, which usually fades, although in some people it persists.

How many sessions might be needed?

It depends on the number and size of the veins. Some people need just one session, whilst others require several.

Can varicose veins come back?

The treated vein may close, but new varicose veins may appear in other vessels, or a section of the vein may reopen.