Warts are caused by the papillomavirus. Genital warts are caused by one strain of the virus, and other warts by a different type of the same virus. Warts, other than the genital type, are transmissible through contact with both infected people and inanimate objects which infected people have touched. You can tell your friend that it is actually very easy to remove warts, although the virus that causes them will live in his system forever. The warts tend to appear when one's immune system is weaker, i.e. when the person is under stress, either physical or emotional.
Warts are perhaps ugly by society's standards, but there are no long term deleterious effects.