Rules: Dragon Immunities

Every kind of true dragon has immunity to at least one type of energy, as noted in the Monster Manual.
A true dragon ignores the detrimental effects of extreme heat (110°F to 140°F) and of extreme cold (0°F to –40°F). A true dragon in these conditions does not have to make a Fortitude save every 10 minutes to avoid taking nonlethal damage.
All creatures of the dragon type are immune to magic sleep and paralysis effects, also as noted in the Monster Manual.
True dragons develop damage reduction as they age, as noted in the Monster Manual. Damage reduction is a supernatural ability and is ineffective in an antimagic field.
True dragons also develop spell resistance as they age, as noted in the Monster Manual.