Jessica Alba's Shoulder-Length Hair

How to Cut the Hair
To achieve this particular haircut, Jessica Alba's hair is layered along the bottom third of the length. This creates shallow layering that tapers the ends and retains fullness in the upper portions of the hairstyle.

To get this type of layering, the hair is elevated to approximately 135 degrees (45 degrees from pure vertical) and cut using a horizontal cutting line. You can also use a 90-degree elevation (straight out to the sides) and a 45-degree cutting angle (scissor tips inward at the top of the cut).
The ends of the hair are point cut to soften the cutting line and provide some lightness and movement along the ends.
The hair Color
Due to her genetic heritage, Jessica's natural color is generally darker. However, aside from the golden blonde she wore as Sue Storm in "The Fantastic Four," she has had a range of flattering colors.
This hair color typically features a level 3-4 base of gold (yellow-orange), giving a chocolaty tone, accentuated and given depth by the addition of caramel tones of level 5-6 in neutral or golden hues. This particular palette is perfect for her complexion and helps to intensify the depth of her eyes.

Jessica's face has a lovely oval shape, and her features are all rounded. Because of this, styling her hair with large, soft waves makes for a perfect counterpoint to the shapes already visible in her features.
While she could easily carry a curlier look, such a style could appear more juvenile. Something styled perfectly straight might tend to make her appear older. This soft-wave look utilizes her natural wave pattern, giving her a youthful yet age-appropriate appearance.
The look is achieved via the use of a diffused dryer and some scrunching for those with natural waves. Those with straighter hair can achieve this wave with large roller tools (or medium tools heavily loaded), while individuals with curly hair can use a flat iron to reshape the natural wave to suit their tastes.
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See also:
Jessica Alba hairstyles
Hair color and skin tone
Cool and warm hair colors