There is little doubt that conditioning the hands can result in both short and long-term damage. All physical training puts a certain amount of stress on the body. We should consider the risks of proper conditioning in this context.
It would be inaccurate and irresponsible to claim that even moderate conditioning eliminates all risk of injury. Any training method capable of producing significant positive results also brings with it the potential for negative side effects. Anyone involved in long-term, strenuous, physical activity is familiar with associated injuries. Like other forms of exercise, injuries from conditioning are most often a result of over-training. When trained over zealously, even things as benign as jumping rope or jogging commonly causes problems such as shin splints.
IMPORTANT- Hand conditioning should not be done by any individuals who may still be growing. As a general rule, this includes anyone under 16 years of age. Some people may have already achieved full size by this age while others may continue to grow for several more years. It is very important to wait until the skeletal system has fully matured before undertaking bone conditioning. The growth points are commonly located at the joints and these points do not fully harden until a certain age. Once they solidify, they do not grow. For this reason, it is extremely unwise to deliberately promote bone hardening and calcification until this process is complete.