皮下 is read as ひか (hika) and means subcutaneous.
ひか
hika
ひかそしき
hypodermis
ひかちゅうしゃ
hypodermic injection
ひかしぼう
subcutaneous fat
かわ
mask (hiding one's true nature)
ひにく
(only) surface
ひふ
skin
かわきり
beginning
ひふびょう
skin disease
ひかく
leather
かわざんよう
over-optimistic calculation
ひふか
dermatology
ひしつ
cortex