Source: Personal experience with Illia as a follower (who likes casting the AoE frost spell, Ice Storm).
Also, this UESP article about Illia seems to back me up:
Illia favors Frost spells. This can be particularly devastating in combat to both enemies and the player, as she frequently uses slow moving AoE Frost spells after about level 20. Players specializing in melee should be particularly careful with her as a follower.
I recommend using measures to increase magic resistance or resistance to the element of the spell that your follower favors using.
List of followers here: http://uesp.net/wiki/Skyrim:Followers
Check out which ones use which types of spells. Note that non-mage followers, that are given staves that cast AoE spells might use them and hurt you too.
You might also want to consider an archer-type ranged follower (Faendal, Aela, etc.), instead. They seem to take extra care not to hit you, unlike their AOE-spell using mage counterparts.