Is an itchy rash around my armpit and spreading to my chest area common after miraDry?

It’s common to experience numbness near your arm pit and palpable lumps early post treatment. They are expected to subside over time. It’s important though to follow up with your treating physician to make sure you are healing properly. As regard to the rash, it’s possible you may experience some type of allergic reaction or this may even be a symptoms of skin infection. Make sure you follow up with your treating physician to make sure that it’s properly treated. A photo of the rash may be helpful as well.
Sincerely,Stewart Wang, MD FACSBoard Certified Plastic SurgeonMedical Director, Wang Plastic Surgery & Med Spa

An itchy rash on 1 (or 2?) armpits and chest, occurring 3 after MiraDry, is not something I’ve seen and I have extensive experience; likely unrelated, even more so if it is just on 1 side. 

The numbness and lumps you are experiencing are most likely common begin side effects that will improve overtime. However, the rash could be a sign of a local reaction, either allergic or infectious process. I recommend you follow up with your provider in order for the rash to be looked at, and to make sure it is being treated properly. Best of luck! 

As you mentioned, lumpiness, numbness are all possible, and should settle down. But an itchy rash is unusual. Itching itself is possible, but should not be troublesome. If you have a rash proper, you should consider letting your doctor know. Alternatively, you could also take an antihistamine for a day and check if that makes the rash better.  If you have any fluid filled vesicles/ blisters/ tingling or pain, do go to the doctor right away.