Skin on your hands, elbows, and knees will dry out and break down from doing things like pad drills and heavy bag and mat work especially during the winter months and I suspect that is what is happening now and why you have this problem.
Why 100 when you know it will cut your skin? When your skin is cut that means you did something wrong. Conditioning does not mean you go until you can see bone to prove you are a tough guy. Conditioning means you work your way up to it. 50 would probably have been plenty and maybe even 10 today and 20 next week and so on. Good conditioning is done without breaking the skin and/or developing a lot of scar tissue. In martial arts common sense too is part of training.
If your skin is dry use some vaseline to keep the skin from splitting. If you take good care of your body it will serve you well for a long time. Abuse it and it will let you know sooner or later.
The elbow is one of the bodies hardest points for impact. the bone is very strong and does not need to be hardened. This may just lead to injury. The best way is to just continue your work on the bags and ice them when you are done to remove swelling and then continue over and over again, this will just form callouses on the skin of the elbow and prepared the muscles and soft tissue to become prepared for some trauma. The actual bone itself needs no hardening.
In time grasshopper
Elbows are better to be trained in lighter bags...They are not like the fists...For example you don't condition your elbows in a wall bag filled with rice, like you do with your fists..You use light bags for that...Is much much healthier....and this has to do with other parts of the body also, not just with the elbows..:)
I have sensitive skin and it bruises and cuts really easy.
My elbows looked really bad after doing a hundred elbows today. I had pretty good form, no not perfect but that wasn't the problem. Will this go away with time?
