Plastic-like/smooth effect

Hi, I'm using photoshop CS5 and I would like to know how I can achieve this plastic-like/smooth effect on a photo? (the smooth skin and those faint lines around the arm area). Can anyone help?


some other examples, again those lines and the slight smooth/blurry effect
 and 
these were taken off some coloring psds I found on tumblr, they are the base image without the coloring so I guess the effect was achieved separately.



Thanks in advance!