In general, running a CPU constantly around 50C will not dramatically reduce its useful lifespan - You are far more likely to replace your PC long before the CPU fails due to the effects of prolonged overclocking.

It will put additional strain on the CPU, which is why you should really replace stock heatsink and fans with higher performance units. These will allow for better heat dissipation and improved airflow, reducing the CPU's core temperature. It's not essential, but if you plan on keeping this machine for the forseeable future, may be recommended to prolong its life.

Just don't lose any sleep over it - As long as you're not exceeding 60C there shouldn't be a problem.