Blisters are extremely rare after either Fraxel Restore or Fraxel Repair. They can be...
1. An allergic contact dermatitis to a numbing cream used before the procedure, or topical antibiotics, such as Bacitracin, Polysporin or Neosporin/Neomycin, or other post operative creams.
2. Bacterial infection (impetigo).
3. Viral Infection of the skin (herpes).
There may be other causes and you should contact your doctor immediately so that you can be evaluated and treated accordingly to prevent progression and possible scarring. I'm sure they would want to know!
Web reference: http://www.thenyac.com/fraxel/index.html