Details and Texturing
To create the texture and stubble around the man’s chin, I zoomed into the image and 'pixelled' these details by hand, as demonstrated in the following stages: 
1.Basic smooth area.

2.I applied small blobs with the dodge t
ool and a small soft brush.

3. Smoothed the blobs with the smudge and blur tools and a soft brush. Touches
of shadow were added between the blobs with the burn tool.

4.Added faint highlights and shadows.

5.Began applying stubble, working over the dark areas using the burn tool and the small
est spatter brush on 20% exposure. 

6.Added light pixels with the dodge tool, using the spatter brush and small hard brushes. Added shadows adjacent to these light dots and darkened the edges of chin with burn tool and soft brushes to gi
ve a rounded appearance. 
The burn tool and spatter brushes were used for the man’s neck and strands of hair were pulled over the top using the smudge tool and small hard brushes. The finer strands were created with a 1 pixel brush on 5-10% pressure.   
I then decided that the shading of the face looked too smooth and plastic, so I decided to indulge in a little hands-on stippling - a technique familiar to most 8-16bit artists. This helped to give the skin a sweaty and porous appearance.
1.Basic airbrushed area.

2.Light and dark areas stipple
d using dodge and burn tools.

3.Additional pixels and blobs added.

4.Smaller light and dark pixels added with burn and dodge
on higher exposure. 
Reduced size - before and after stippling.
The beads of sweat were also pixelled in zoom mode, using the following methods:
1.Basic smooth area.

2.Various sized blobs dotted over skin
with the dodge tool on highlights setting.

3.Burn tool and 1pixel sized brush used to apply shadows around each dot and blob.

4.Smudge tool used to extend larger beads to look like dr
ips. 1 pixel highlights added to the blobs.

5.Strengthened highlights and shadows and added random light and dark pixels with dodge and burn tools.

Some of the more subtle droplets were created using the following method:
1. Faint circles made with burn tool (1 pixel brush) on low exposure.

2. Dodge tool used to fill each circle.

3. 1 pixel highlight added to lowe
r half of circle using dodge tool on highlights setting.

Actual Size
Using this technique, I added droplets of sweat to the man’s stippled face and ended with the following stage:

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