Lactic acid does not contain lactose. In fact, none of the "lac" ingredients
in foods do.

Exact information on this is hard to come by. I've collected some expert
opinions on The Experts Speak page in my web site.
http://ourworld.compuserve.com/homepages/stevecarper/experts.htm

You can also check through the rest of the Dairy Facts section for more info
on milk names and ingredients.

Steve Carper
Steve Carper's Lactose Intolerance Clearinghouse