When you are changed by magic, your skin also toughens.

Prerequisite(s): Con 13.

Benefit(s): Whenever a transmutation spell or spell-like ability affects you, your natural armor bonus increases by 1. If you have no natural armor bonus to Armor Class, treat your natural armor bonus as 0 for the purposes of this feat. The bonus to your natural armor bonus increases by 2 if the caster level of the effect is 10th or higher.