Brown stains on skin after working with Tollens' reagent I was working in the lab preparing Tollens’ reagent. When I came back home, I observed that my fingertips were brown, and I tried to wash it with soap several times but it didn't work.

It has been a day and they don't seem to go. 

What may have been the reason? Is it permanent and how can I get rid of it?
The stains are due to silver nitrate, the reactive portion of Tollens’ reagent. It is very prone to reduction to metallic silver.

If you got it on your hands (a clear signal you weren’t wearing gloves when you should have been) it will create small silver particles in your skin — this is why it won’t wash off. Since the particles are small, they don’t exhibit the classical metallic characteristics (looking silvery, reflecting etc).

Don’t worry, they will grow out within a week’s time or so, due to your skin renewing itself.
And wear gloves next time.