Will Fraxel Laser Tighten Under Chin Area? I Have Lost Around 90 Lbs.

Fraxel is a brand name like Chevrolet or Toyota.  There are a few different lasers that carry the Fraxel brand and many, many lasers made by other manufacturers that perform fractional resurfacing.  That said, none of the fractional resurfacing devices made by Fraxel or any other manufacturer are liable to produce substantial improvement in loose skin under the chin.  Most likely a surgical procedure will be needed to help you achieve the best results.

 You describe excess skin under the chin post weight loss. This excess skin will not respond to liposuction, laser lipo ,thermage or fraxel. You need a consultation bey a board certified plastic surgeon to examine you and give you the best option. Your picture can be helpful.

Fraxel will do a lot of great things, but it won't significantly tighten loose skin from aging or weight loss. sorry....... sounds  like you might need a neck/facelift surgical procedure.