Sony a77 noisy skin tones at low ISO ?

I am generally enjoying my a77 but am finding it a bit frustrating that even when shooting at ISO 100 and being careful to avoid under-exposure I am finding some luminance and chroma noise in white caucasion skin tones when a model is not looming large in the image - e.g. in what you might call "environmental portraits". I know that 24MP is crammed onto an APS-C sensor, but this has surprised me a bit that I am getting this at ISo 100. Anyone else ?

--
"When words become unclear, I shall focus with photographs. When images become inadequate, I shall be content with silence." Ansell Adams.