I have a reaction in inner thigh from VenaSeal. I'm taking prednisone and using a heating pad, how long will this last? (photo)

This is temporary problem (1-2 weeks) which is more common in patients which allergies to adhesives, such as tape. It is generally a histamine related inflammation, thus topical or oral Benadryl can dramatically help resolve this before steroids are necessary. The heating pad will make this worse.
Either way, you are passing through this difficult problem and it should completely resolve with Benadryl, compression, and steroids.

Redness and inflammation is not common with Venaseal. As Dr. Powell suggested also, Benadryl will definitely help with the redness and swelling. Venaseal is a wonderful new treatment that stops venous reflux at a high rate. Unfortunately, some may not know how their body/skin will react to the glue until afterwards. It is nothing to panic about, it should go back to normal in a short amount of time. Best of luck to you. - Dr. Haney

Usually days to weeks but can certainly take much longer. Please see your provider for follow up until complete resolution !!