You can create a Ptex-based map to mask out areas of the mesh that you do not want splines to appear. In this example, a mask is created to define the character's hairline.
Click the Primitives tab.
In the Generator Attributes section, click
beside Mask then select Create Map from the menu that appears.
This sets the number of texels per-face for the Ptex map.
This sets the map value to 0, which masks out the mesh surface so no splines generate. When painting on the mesh, you use white. This sets the painted areas to 1, which generates splines on the surface.
in the Tool Box to open it.
icon to save the Ptex map. 
You can modify the map by clicking this
icon beside Mask, paint on the mesh, and then click
to save your changes.