Drawing Hair in Photoshop
In this tutorial, we will give this basic human form:

a full head of hair like this:

Using the brush, dodge, burn and smudge tools. This technique works best on mostly straight or slightly wavy hair.


Laying out the basic color
In this example, we are creating medium-brown hair, so draw in the basic shape of the hair with a hard edged brush with medium brown. Follow the contours of the head and shoulders, making the hair flip at the ends as desired. Don't worry about being perfect, but make sure that the head itself is covered fully with no gaps.

Smudging the edges Part One
Using a small-ish brush with a soft edge (approximately 10-20 px) at about 85 to 95% strength, smudge the edges of the hair to flow and fall naturally against the face, shoulders, neck and back.
Here are the directions I smudged:

to form this:

Dodge & Burn Part One - Individual Strands
This part is the most tedious, but it actually does go by rather quickly and painlessly.
Select the dodge tool set to midtones, around 15 to 20% strength and a 2 to 4 pixel brush. Start drawing in highlights in the direction that the hair naturally grows. You may want to look at a source image for this. Switch the setting to highlights and repeat. This varies the colors and luminosity of the hilites, making the hair appear more natural.

Now hold down the alt button and the dodge tool becomes the burn tool. Repeat as above, switching between highlights and midtones to vary the color and luminosity of the lowlites.

If it's not looking the way you want it to, vary something: increase/decrease brush size, switch brush shape, increase/decrease strength, switch modes (shadows/midtones/highlights).
Here's what I had after about 5 minutes of work:

Dodge & Burn Part Two - Lighting Source
Now that we have the individual strands drawn in, it looks flat. To put the head of hair in a realistic environment, consider the source of light. Here, it is coming from the front/left, so we want to highlight the front and darken the back. We also want to highlight natural contours of the head and thin-ness of the ends of the hair.

Here are the areas I've highlighted and darkened with a large (approx. 50 to 100 px) soft edge brush with dodge and burn.

Try different dodge/burn modes to match your lighting source:
- Dodge Midtones gives less saturated, whiter highlights
- Dodge Highlights gives more saturated yellower hilights - Burn Midtones gives more saturated shadows in keeping with the base color
- Burn Highlights gives less saturated, gray/black shadows

Use all in combination to achieve a more natural look:

Smudging the edges Part Two
The final step is to smudge out any harsh edges, mostly at the tips of the hair where it meets the face and shoulders.

I like to use a large spatter brush for this, set to about 60% strength, for a wispy look.
The final image after smudging:
This example took me about 8 minutes to produce, but you can always spend more time tweaking strands and highlights. If you're working on a larger image, it will take longer.

Further ways to tweak the hair:

- duplicate the hair layer and adjust the hue/saturation, then vary the opacity or blending mode of the adujsted layer. (I usually like to use overlay or one of the light modes.)
- duplicate the hair layer and vary the contrast using curves or levels, then vary the opacity or blending mode of the adjusted layer as above.
- use the sharpen and blur brushes to vary the focus of highlighted or shaded areas of the hair.