In Borderlands 2 you can customize each character class with different heads and skins. The heads have different hair styles faces, accessories etc.. every character class has over a dozen heads to be unlocked. unlocking heads is pretty easy and eventually you will get all the heads that are available. The missions below always have a head reward (sounds weird?.. lol) but the enemies/bosses do not, they drop heads at random just like they would guns its pretty random but we don’t think there is a “rare” head that is impossible to find. All character classes have Heads that can be unlocked, Axton, Maya, Salvador and Zero.
Skins are pretty much what they sound like, they are clothing for your character and can be found pretty much the same way by completing missions, drops, loot etc.. These are available for all character classes: Axton the Commando, Maya the Siren, Salvador the Gunzerker and Zero the Assassin.
Vehicle skins are found on enemy drops and loot piles.
Unlocking Heads:
Unlocking/Getting Skins
Missions with Skin Rewards: