6 weeks out from a brachioplasty is still fairly early, so some segments of the scar, especially those that are under more tension or nearer to mobile areas such as the armpit, can have a little more redness/tenderness. Make sure to consult your surgeon to determine if there is an element of wound healing issues or infection before using any topical treatments. If there is no infection or open area, starting a scar treatment regimen at this point is not a bad idea. There are a lot of over the counter treatments available, and the jury is out as to what is the most effective. Some people swear by silicone gel or sheeting, others by vitamin E, coconut oil, emu oil, etc, while others say that paper tape works the best. As long as you don't have an adverse reaction to any of these they are all reasonable to try.