Henna works best if you apply it as soon as your feet start feeling hot -- or even before! If your hands or feet are Grade 3, you have to let them heal. Henna will help, but you have to get off those feet. You may have to delay Xeloda or reduce the dose.
I've tried quite a few things to help heal. Here's what works for me when it's really bad.
First, a ten day dose of tapered steroids. This is as unproven as henna, scientifically, but it helps me. Soaking my feet in cool water reduces the pain for the moment. On the worst areas, I apply an antibiotic ointment such as Neosporin or Bacitracin. (Those are the names in the US. If you let me know names in other countries I am happy to post them here.) I let it soak in, then apply Balmex -- a diaper rash cream loaded with zinc oxide -- or a band-aid. Then put a towel on your bed or recliner and get off your feet.
As your feet start to heal, henna can do its job best.