Itching is common immediately after a sclerotherapy treatment. Which is why we apply a potent topical corticosteroid immediately after treatment under the graduated compression stocking. Though itching after sclerotherapy may be a sign of an allergic reaction, there are also several other reasons for what you are experiencing. If you are overly concerned, I'd recommend seeking help from your treating physician or get a second opinion from an experienced cosmetic dermatologist specializing in sclerotherapy. Because the natural reaction of the body upon injection of the sclerosing agent may be to release histamine, itching can ensue. If you are experiencing other symptoms like swelling, discoloration, or severe discomfort, it's important to seek help. As a double board certified dermatologist and cosmetic surgeon, I would suggest that you make sure you speak with a professional.