25-35% TCA does great for knees and elbow but often need repeating.
TCA peels are wonderful to even out color problems for knees and elbows but often need repeating until the color looks even. It is easy to undergo.
Thank you for your question. Rough and darker skin is common on peoples elbows and knees. There are various creams that your dermatologist can prescribe you with either Urea, Salicylic acid or Ammonium Lactate that can be used to help soften and lighten up these area. I would recommend you make an appointment with a board certified dermatologist to get you in the right direction.