Sclerotherapy is considered safe for most people and has been used for decades to treat spider veins and small varicose veins. The procedure has clinical success rates of 80 to 90%, and serious complications are uncommon. That said, it does carry real risks that range from expected cosmetic side effects to rare but significant events like blood clots, so understanding the full picture matters before you decide to go through with it.
What Happens During the Procedure
Sclerotherapy works by injecting a chemical solution directly into the targeted vein. The solution damages the inner lining of the vein wall, triggering inflammation. Platelets cluster at the damaged site, cellular debris and fibrin build up, and the vein seals shut. Over time, the body replaces the closed vein with fibrous connective tissue, and blood reroutes through healthier veins nearby.
The agents used come in two main forms: liquid and foam. Foam versions cause the vein walls to spasm and press together, which increases the chance the vein stays permanently closed. With foam or liquid detergent-based agents, the damage to the vein lining happens within minutes and can spread slightly beyond the injection site. The FDA-approved agent polidocanol (sold as Asclera) is indicated for spider veins up to 1 mm and reticular veins between 1 and 3 mm in the legs.
Common Side Effects Most People Experience
The most frequent side effects are local and temporary, but they’re not subtle. In the clinical trial for polidocanol, 42% of patients developed bruising at the injection site, 41% had irritation, and 38% noticed skin discoloration. About 24% reported injection site pain, 19% had itching, and 16% felt warmth around the area. These numbers are high enough that you should expect at least some combination of bruising, discoloration, and soreness after treatment.
Skin darkening, or hyperpigmentation, is one of the side effects people find most frustrating because it can linger. It shows up in about 30% of cases, and how noticeable it is depends on your skin tone, the type of agent used, and how well you follow post-treatment care instructions. For most people, it fades on its own over weeks to months, though in some cases it can take longer.
About 8% of patients in clinical trials developed new tiny blood vessels near the treatment area, a phenomenon called matting. And roughly 6% had small, localized clots at the injection site, which are different from the deep vein clots discussed below.
Serious Risks to Know About
Deep vein thrombosis (DVT) is the most significant safety concern. In a study tracking outcomes across 1,000 legs treated with ultrasound-guided foam sclerotherapy, DVT occurred in 1.5% of cases overall. Only 0.2% of those were symptomatic, meaning the patient actually felt something was wrong. The reported range across studies is 0% to 5.7%, depending on the technique and patient population. These clots can potentially travel to the lungs and cause a pulmonary embolism, which is why the procedure is off-limits for anyone with an active blood clot condition.
Severe allergic reactions, including anaphylaxis, have been reported in post-marketing surveillance. Some of these cases were fatal. The risk increases with larger injection volumes (above 3 mL), which is why practitioners keep doses as small as possible. If you have a known allergy to polidocanol or similar agents, sclerotherapy is contraindicated.
Other rare complications reported after the procedure reached the market include stroke, migraine, loss of consciousness, confusion, and tissue death at the injection site. Accidental injection into an artery rather than a vein can cause severe tissue damage, ischemia, or gangrene. These events are rare enough that they didn’t show up in controlled clinical trials but have appeared in real-world use.
Foam vs. Liquid: Is One Safer?
Foam sclerotherapy tends to be more effective, with over 90% of treated vessels resolving. But the foam format introduces a specific concern: visual disturbances. In one study comparing the two approaches, 2.5% of patients receiving foam experienced brief visual disturbance lasting less than two minutes. None of the patients in the liquid group had this issue. The episodes are typically short-lived, but they can be alarming. If you have a history of migraines with visual aura, this is worth discussing with your provider beforehand.
How Much It Hurts
Pain levels vary depending on the sclerosing agent used. In a study comparing hypertonic saline alone to saline mixed with a numbing agent, about 62% of patients receiving plain saline rated their pain as none or mild. When a local anesthetic was added, that jumped to over 90%. Most practitioners today either use agents with built-in anesthetic properties or add lidocaine to reduce discomfort. You can generally expect a stinging or burning sensation at each injection point, but the procedure doesn’t require sedation or significant anesthesia.
Recovery and Compression
After treatment, you’ll typically wear compression stockings or bandages. Protocols vary, but a common approach involves wearing a bandage for the first 24 hours, then switching to compression stockings during the day for one to two weeks. Some providers recommend wearing them around the clock for the first week. There’s no universally agreed-upon schedule for exactly how many hours per day you need compression or for how long. Clinical guidelines recommend compression as a first-line part of recovery but don’t specify an exact daily duration, so your provider’s instructions will depend on their experience and your specific situation.
Walking is generally encouraged soon after treatment to promote blood flow. Strenuous exercise, hot baths, and prolonged sun exposure on the treated area are typically restricted for a period your provider will specify.
Who Should Avoid Sclerotherapy
Sclerotherapy is contraindicated if you have an active blood clot in a deep vein, a known allergy to the sclerosing agent, or are pregnant. People with clotting disorders need careful evaluation because the procedure inherently involves creating controlled clotting within treated veins. If you’re bedridden or unable to walk, the increased DVT risk makes the procedure less appropriate.
How Effective It Is Long-Term
When performed correctly, sclerotherapy resolves 90% or more of treated vessels. Most people need multiple sessions to clear all visible veins, especially if they have spider veins spread across a large area. Treated veins don’t come back, but new spider veins or varicose veins can develop over time in different locations, particularly if you have underlying venous insufficiency or genetic predisposition. This isn’t a failure of the treatment; it’s the nature of the condition.
For small spider veins and reticular veins, sclerotherapy remains the gold standard. The procedure has a strong safety record when performed by experienced practitioners on appropriate candidates, and the vast majority of side effects are cosmetic and temporary. The serious risks, while real, are statistically uncommon.