I believe they only do so against force effects...I could be wrong though.
Touch Attacks: Some attacks completely disregard armor, including shields and natural armor—the aggressor need only touch a foe for such an attack to take full effect. In these cases, the attacker makes a touch attack roll (either ranged or melee). When you are the target of a touch attack, your AC doesn't include any armor bonus, shield bonus, or natural armor bonus. All other modifiers, such as your size modifier, Dexterity modifier, and deflection bonus (if any) apply normally. Some creatures have the ability to make incorporeal touch attacks. These attacks bypass solid objects, such as armor and shields, by passing through them. Incorporeal touch attacks work similarly to normal touch attacks except that they also ignore cover bonuses. Incorporeal touch attacks do not ignore armor bonuses granted by force effects, such as mage armor and bracers of armor.
Mage Armour and other force armour effects only affect your touch AC against incorporeal touch attacks. They won't help you against, amongst other things, spell touch attacks or ranged touch attacks like acid flasks.