Abstract
The initial shape and early evolution of H II regions are controlled by the density distributions of star-forming cloud cores. We briefly discuss the effects of dust and decreasing density gradients on the observed properties of UC H II regions, and on the new class of Super-ultra-compact H II regions. Dust absorption can effectively reduce the size of the photoionized region, and density gradients can modify the spectral index of the emission. The effects of the density gradients also seem to be present in extragalactic H II regions.
