Sclerotherapy guide: injections for spider veins and small varicose veins

Sclerotherapy is the injection of a chemical solution directly into unwanted blood vessels — spider veins, reticular veins, and small varicose veins — causing endothelial damage, vessel fibrosis, and gradual clearance. It has been performed since the 1930s, has the most robust evidence base of any leg vein treatment, and remains the gold standard for superficial lower extremity vascular lesions. Here is the complete guide.

The mechanism: sclerosant-induced endothelial damage

How sclerosants close veins

A sclerosant solution injected into a blood vessel:

Contacts the vascular endothelium (the single-cell inner lining of the vessel)
Damages the endothelial cells through detergent action (surfactant sclerosants) or osmotic/chemical injury
The damaged endothelium triggers the coagulation cascade within the vessel → thrombosis of the vessel lumen
The thrombus organizes → fibrous replacement of the vessel → the vessel collapses and is gradually absorbed over weeks to months

The result: the treated vessel disappears as it is replaced by fibrous scar tissue and cleared by macrophages. The blood that previously filled the vessel is rerouted through adjacent functioning veins.

Sclerosant types

Polidocanol (Asclera, Aethoxysklerol): The most widely used sclerosant in the US and Europe. A detergent (surfactant) that disrupts endothelial cell membranes. FDA-approved for spider veins (0.5%) and reticular veins (1%). Lower pain and bruising than STS for many patients; allergic reactions very rare.

Sodium tetradecyl sulfate (STS, Sotradecol): Another surfactant sclerosant. FDA-approved; slightly more efficacious than polidocanol at equivalent concentrations for larger vessels; slightly higher pain and bruising rate. Widely used for reticular and varicose veins.

Hypertonic saline: Osmotic sclerosant — creates osmotic damage to endothelial cells. No FDA approval as a sclerosant (used off-label); more painful than detergent sclerosants; rarely used as first-line.

Liquid vs. foam sclerotherapy

Liquid sclerotherapy

Standard technique: the sclerosant solution is injected as a liquid. Displaces a small volume of blood in the vessel at the injection point.

Best for: Spider veins (0.1–1.0 mm) and small reticular veins (1–3 mm) — the vessel diameter is small enough that liquid sclerosant contacts the entire endothelium without significant dilution.

Foam sclerotherapy

The sclerosant is mixed with air or physiological gas (CO2/O2) using a two-syringe technique (Tessari method) to create a foam. The foam:

Displaces blood more completely than liquid (greater surface contact with endothelium)
Allows lower sclerosant concentrations to achieve the same endothelial effect
Provides better visualization under ultrasound guidance

Best for: Larger reticular veins (2–6 mm) and small varicose veins where liquid sclerosant would be diluted by the larger blood volume. Ultrasound-guided foam sclerotherapy (UGFS) treats truncal varicose veins and perforator veins not visible at the surface.

Foam sclerotherapy limit: The foam volume per session is limited — large foam boluses carry risk of air/gas passing into the venous circulation → transient visual disturbances or neurological symptoms in patients with patent foramen ovale (PFO). Most guidelines limit foam to 10 mL per session.

The procedure

Injection technique

Treatments are performed with the patient in the supine or semi-prone position (legs slightly elevated to empty veins). Spider veins are injected with 30–32 gauge needles; larger vessels with 27–30 gauge.

Each injection point delivers a small volume (0.1–0.5 mL for spider veins; 0.5–2 mL for reticular veins) directly into the vessel lumen. A skilled sclerotherapist will blanch the vessel immediately on injection — confirming correct intraluminal placement.

Session coverage: A typical spider vein session treats 20–50 injection points across one or both legs; 20–60 minutes total.

Compression post-treatment

Compression is applied immediately after treatment and worn continuously for 24–72 hours (and during daytime for 1–2 weeks for larger vessel treatment):

Collapses the treated vessel walls together → promotes fibrosis without thrombus organization
Reduces post-treatment pigmentation (hemosiderin deposition from extravasated blood)
Reduces the risk of trapped blood ("trapped hematoma") in treated vessels

Compression stockings (20–30 mmHg class II) are the standard post-sclerotherapy recommendation. Walking is encouraged immediately — calf muscle pump action clears residual sclerosant and reduces deep vein thrombosis risk.

Risks and side effects

Hyperpigmentation (hemosiderin staining)

The most common aesthetic complication: brown discoloration at the site of treated veins from hemosiderin (iron) deposits following erythrocyte breakdown in the treated vessel. Occurs in 10–30% of patients to varying degrees.

Resolves in: 3–6 months in most patients; can persist 12+ months in some. Compression post-treatment is the most effective preventive measure. Treatment with IPL or Q-switched laser if persistent.

Matting (telangiectatic matting)

A fine red network of new tiny capillaries appearing around treated veins in 10–15% of patients — paradoxically, sclerotherapy occasionally stimulates new vessel formation adjacent to treated vessels. Usually resolves within 3–6 months. Treating the feeder reticular vessels (which drive the spider vein network) reduces matting risk.

Thrombophlebitis and deep vein thrombosis

Superficial thrombophlebitis (inflammation of the treated vein) is common and expected — the mechanism of sclerotherapy. Painful, hard, red cord along the treated vessel that resolves in 1–4 weeks.

True deep vein thrombosis (DVT) is rare (< 0.1%) when performed correctly. Risk factors: thrombophilia, immobility post-treatment. Walking post-treatment significantly reduces DVT risk.

Ulceration

If sclerosant extravasates outside the vessel (perivascular injection), local necrosis and ulceration can occur. Risk minimized by precise intraluminal injection and appropriate concentration for vessel size.

Sclerotherapy vs. Nd:YAG laser for leg veins

	Sclerotherapy	Nd:YAG 1064 nm Laser
Mechanism	Chemical endothelial damage	Selective photothermolysis
Best vessel size	0.1–6 mm (all spider + reticular)	0.3–3 mm (smaller vessels)
Pain	Mild stinging at injection	Moderate heat sensation
Downtime	Minimal; compression required	Minimal
Hyperpigmentation risk	10–30%	10–20%
Cost per session	Lower	Higher
Sessions needed	1–4	2–5
Evidence	Gold standard; 85+ years	Good; less evidence vs. sclerotherapy

Clinical consensus: Sclerotherapy is the first-line treatment for most leg spider veins and reticular veins. Nd:YAG laser is preferred for: very fine vessels (< 0.3 mm) too small for injection; needle-phobic patients; vessels that did not respond to sclerotherapy; facial vascular lesions (where sclerotherapy is not used).

Realistic expectations

Sessions needed: Spider veins typically require 2–4 sclerotherapy sessions at 4–6 week intervals. Not all vessels clear completely; 70–90% clearance is a realistic goal.

Timeline for results: Treated vessels gradually fade over 4–12 weeks. Full results not visible for 3 months after the last session.

Recurrence: Sclerotherapy permanently closes treated vessels — they do not return. However, new spider veins continue to develop over time (genetic predisposition, hormonal factors, prolonged standing). Maintenance treatment every 1–2 years is common.

Looking for a sclerotherapy or vein treatment provider? Browse med spa providers on MedSpot →