Ultimate Iron Man #1 reveals that Tony Stark’s genius is caused by an accident his mother (brilliant scientist Maria Cerrera, who names him Antonio) suffered while she was carrying him in her womb. He has neural tissue throughout his body, as if his entire body is a brain, giving him tremendous mental capacity but at the cost of chronic pain akin to severe burns due to the over stimulation of neural cells in his skin. His father uses a newly invented biological armor to ease Tony’s pain.
Despite the pain, he is endowed with regenerative capabilities due to the same mutation that caused the neural cells to differentiate all over his body. The biotechnology armor is constructed out of genetically modified bacteria that are able to group together to dissipate kinetic energy when impacted upon, and is able to dissolve any metal that can be oxidized. The disadvantage of this biotech armor, however, is that it will dissolve the wearer’s skin after a few hours and will need to be washed off with water and soap.