rough skin, rough
皶 centers on skin that is rough or coarse in texture, lacking smoothness.
皶 combines 查 (which may contribute a phonetic element) with 皮 (skin), suggesting a character related to skin condition. The exact historical development is uncertain.
The left side 查 looks like a wooden inspection tool, and the right side 皮 is skin. Imagine inspecting skin with a rough wooden tool and finding it coarse and rough.
For サ, picture rough skin after a long day in the sun: sun -> サ, and the sun leaves your skin feeling rough.