Does fractional CO2 laser thin the skin?

Dear RS Doctors, I have heard here and there (including from doctors) that they're not inclided to used the fractional CO2 laser on skin between 30 and 40 years old, because it 'thins the skin' (or at least after several repeated sessions). I guess my question is a) Does it really, and is there any scientific evidence of this, and b) If it is something that happens only on repeated treatment, what is the upper limit of CO2 sessions one should have? Thanks.