I've spent the morning playing with noise in both illustrator and photoshop, blending layers and testing various grain textures - trying to get close to this type of superbly fine but crisp noise but it ain't working - the black noise in many places (see the teeth and lips) boggles me. Is anyone here that knows how this was done?
It looks like either real film grain, or simulated film grain. There's no way to tell how it was done, since there's no EXIF data present to tell even which application was used.
One of the easiest ways to add film grain in Photoshop is to use the Camera RAW filter.
Open an image in Photoshop, right click the image layer, and convert to a Smart Object.
Click Filter > Camera RAW filter. Then when the filter dialog opens, click on the "Fx" tab, and add some grain.
The good thing about this functionality is that it's non-destructive. You can edit the filter and change the amount of grain without destroying the original image.
To copy the effect I made a snippet of the image. It has at left a slice of the original and the rest has been cleaned with noise reduction, actually median filtering a few times.
The cleaned version has an adjustment layer (with. full white layer mask) It's adjusted to darken the image as much as the grains do, but affecting to the colorfulness quite little (=straight line, nearly 45 degrees) It can be readjusted later if needed.
Then, the layer mask of the adjustment layer got grain:
The result after tweaking the curve a little and lifting a little the contrast of the cleaned image to compensate the darkness caused by the original grain (see, the histogram is a little stretched to the right):
Unfortunately the details of the cleaned image cannot be restored to same glossines than the original, noise reduction removed details, only compensating the darkness of the original grain was possible.