Toughening up skin (in the physical sense not the emotional sense) is something that I've considering recently. I've been trying to toughen up the skin on my knuckles (by lightly punching a piece of pine wood from a few inches away, 360 times on each fist once every other day) because I want to have tougher skin, not baby soft skin.
Tougher skin comes from exposing the skin to increased abrasion over a sustained period of time. Think of the way that using a shovel for a few hours a day can cause callouses to build up on the palms of your hands, or walking on your bare feet causes callouses to develop on the soles of your feet.
It's like the saying goes 'you are what you eat', well the same principle applies to everything that your body and mind consume, whether it's food via your mouth, music through your ears, or images through your eyes, it's all consumed by your body so it all has an effect. A man listening to Coldplay will develop differently to one that listens to Metallica. So a man wearing smooth velvet gloves every day will develop differently to one who wears hardy workman's rigger gloves.
People also (subconsciously) judge you by how tough or soft your skin is when you shake hands with them. A man with callouses on his hands and a firm handshake in more likely to get respect from someone than if he had soft hands and a limp handshake.
I searched the net to see what other people did, and some folks over here have tried a few different approaches which are all based on abrasion: shoving their hands in buckets of sand, doing lots of manual labour (using trowels, shovels etc), anything to expose their hands to abrasive contact with a hard material.
(NB. I'm not a medical professional, and I don't encourage anyone to go around punching doors until their knuckles bleed and they break their bones. Skin and muscle repairs itself faster and better than bone does (several weeks versus several months), and joints don't repair themselves at all.)