The successfully closed veins from sclerotherapy contain blood, and blood contains iron. As the vein shrinks, iron is released into the skin where it causes a brown discoloration; this is called “post-treatment hyperpigmentation.” The iron is slowly removed by the body’s natural scavenging system (the reticuloendothelial system) for recycling into new blood cells. People vary greatly in the efficiency of this “mopping up” operation. This causes some people to have very little discoloration that disappears quickly in a few weeks, while others have darker discoloration that takes months to disappear.
Using depigmenting prescription creams which kill off melanin-producing skin cells may temporarily mask this process, but eventually leave permanent white spots because they don’t work directly on the iron deposits, which eventually disappear.