Is Botox good for firming and lifting skin? I'm 36 year old ,but my eyelids and skin already sagging!

With good technique Botox can be used to add a slight lift to eyelids /  brows. An in person assessment is required to make an accurate assessment. In some cases an upper lid blepharoplasty is the best solution. Schedule a consultation with a board certified plastic surgeon who is able to recommend all surgical and non- surgical treatments specific to your aging process.  

Botox is a wonderful product to treat dynamic wrinkles of the face and neck. However, it is not meant to help with sagging skin.  For someone who is 36, I would recommend Ulthera as a non invasive method of tightening skin and muscle.