Hi
Yes ,its seems like blunt razor injury with thermal burn due to hot steam exacerbated by frictional injury.i would suggest to stop shaving the underarm for few days as well as stop using products like antiperspirant ,deodorant etc. keep the area Dry and clean using mild soap and patting it dry, also apply baby power to avoid the friction in the area. You can also use mild over the counter hydrocortisone cream to alleviate the inflammation. In case of infection you can also use anti fungal or antibacterial preparation.