The majority of sclerotherapy sessions pass off without any problems and the patients get a good result with the treated veins disappearing. However, like with every medical technique, there can be problems and complications in practice. Fortunately these are rare but the do happen from time to time.

Most of the complications caused by sclerotherapy are related to the inflammatory reaction created by the sclerosant chemical. Inflammation is what the chemical is supposed to create and, as long as the drug in injected into the vein to be treated there is usually no problem. If however the chemical is injected outside the vein or leaks out of the vein in large amounts, the inflammation can damage the skin. This is called ‘extravasation’ of the chemical.

In most cases if a weak solution of the drug is used (0.2% STD), there is little trouble – occasionally a patient may develop a small blister on the skin or rarely a small sore which will heal up over a few weeks. If however the strongest 3% solution has been injected just under the skin and not into a vein, a serious reaction can occur this can create permanent scarring of the skin.


The more common complications with sclerotherapy relate to prolonged bruising and soreness of the treated vein. The chemical most commonly used in sclerotherapy in the UK is called Fibrovein. Fibrovein is a detergent by its chemical nature – the strongest 3% solution feels soapy to the touch. Fibrovein makes the inside of the vein inflame and become rough – this in turn makes the blood inside the vein clot (or thrombose in medical language). It is this thrombotic process that eventually makes the veins disappear. However during this process, especially in larger veins, the patient can feel quite lumpy and sore over the area of the treated vein. This is due to a prolonged inflammatory reaction potentiated by the presence of clotted blood in the vein. Fortunately this is quite easy to sort out – for most patients the use of anti-inflammatory creams or tablets will soothe the pain until the body resolves the situation naturally. Some patients fine Arnica and other herbal remedies useful. Sometimes it is helpful for the doctors to make a small nick in the skin over the vein to allow the trapped blood to drain out of the vein. This makes the lump go away and usually resolves the inflammation quite quickly.

After treatment most patients will have a bit of skin marking or staining – this is usually a brown mark where the vein used to be and it can take several months to fade completely. In very rare cases a complication called telangectatic matting can occur, where the area that was injected then develops lots of tiny red thread veins as a reaction to the inflammation. These tiny veins are really difficult to treat with further injections as they are too small to get a needle into and are usually best resolved by use of skin lasers or intense pulsed light (IPL) machines.

The wider use of foam sclerotherapy to treat larger varicose veins has produced a few more complications to add to the list. These occur when the sclerosant or the gas that it is mixed up in travel through the circulation to the heart, lungs and brain. There have been reports of small strokes and visual disturbances occurring in patients who have had large veins treated with large volumes of foam sclerotherapy and advanced MRI studies undertaken in the USA have shown that large amounts of foam injected into varicose veins do appear in the general blood circulation quite quickly. It is for this reason that we are very cautious about using foam sclerotherapy for larger veins and prefer to use the technique only for small varicose veins and thread veins.