The endothelium as the target
The endothelium is not just a passive lining. It regulates blood flow, inflammation and clotting, acting as a dynamic interface between circulating blood and the vessel wall. Sclerotherapy works by deliberately disrupting this layer. A sclerosant — typically a detergent or osmotic solution — is injected directly into the vein. This agent interacts with endothelial cells, damaging their membrane structure and triggering cell death. This is not incidental damage, it is the intended starting point of the treatment.
From chemical injury to controlled fibrosis
Once the endothelium is disrupted, a sequence of events follows:
• exposure of subendothelial collagen
• activation of the coagulation cascade
• initiation of an inflammatory response
This leads to endofibrosis, where the vein is gradually replaced by fibrous tissue.
Over time, the vessel no longer functions as a conduit for blood. It becomes a closed, fibrotic cord that is eventually resorbed by the body. This is why the outcome is not temporary collapse, but structural transformation of the vessel.
Why “controlled” is the critical word
The effectiveness of sclerotherapy depends on achieving sufficient endothelial damage without extending that effect beyond the target vein. This balance is influenced by:
• the type of sclerosant used
• its concentration
• the duration of contact with the vessel wall
Too little interaction and the vein may recanalise. Too much, and surrounding tissue may be affected. Modern practice is therefore defined by precision of delivery and dosing, rather than simply the presence of the agent.
A vascular intervention, not a surface treatment
Although often used for visible veins, sclerotherapy operates at a vascular level. It alters blood flow by removing dysfunctional superficial veins from the circulation. Blood is naturally redirected into deeper, healthier vessels. This is why it is considered a functional as well as aesthetic intervention, particularly in cases of venous insufficiency.
A predictable biological sequence
From injection to resolution, the process follows a consistent pattern:
- endothelial injury
- inflammation and thrombosis
- fibrosis and vessel closure
- gradual resorption
Understanding this sequence helps explain why results evolve over time rather than appearing immediately. It is not a cosmetic effect applied to the surface. It is a biological restructuring of the vessel itself.