I had Arthroscopic surgery to fix two tears on my right knee on July 27,2010.
After 2 weeks, started to have redness and itching around the 2 suture sites under the sterile strip. Because it was weekend, cannot consult the doctor, appled Neosporin ointment on it. On 8/16, went to see the Orthopedic surgeon and he determined it was an allergic reaction to Mastisol based on the pattern of the redness. I was advised to take Benadryl should clear up after 2 days. The redness and irritation grew wider than the original size. On 8/20 went to consult a Dermatologist and was prescribed Clobetasol ointment to apply 2 times a day and Vanicream soap bar for cleansing. The rashes turned progressive with a few blisters and spread even wider than before. The original rashes now turn from red to darker in color (almost like purplish).
That's quite a reaction. I posted a link to another persons experience with Mastisol. Some photo's are posted - she had an extreme reaction was well and used oral benadryl as well but it cleared up faster. She also used cold compresses which I assume that you've done. I can't remember if you mentioned in your post if you've seen a dermatologist but that might be a good idea.