Which statement about the skin's barrier function is true?

Which statement about the skin's barrier function is true?

• A. It lacks protection from UV light
• B. It acts as a permeability barrier
• C. It is only for temperature regulation
• D. It prevents all water loss

Answer: (B)

The main idea tested is what the skin’s barrier function actually does. The skin’s barrier is best described as a permeability barrier: the outermost layer, the stratum corneum, forms a tight, lipid-rich shield that limits the diffusion of water and chemicals into the body and helps keep internal fluids from evaporating away. This brick-and-mortar arrangement—corneocytes as “bricks” and lipids (ceramides, cholesterol, free fatty acids) as the “mortar”—creates the hydrophobic environment that reduces transepidermal water loss (TEWL) and blocks many externally encountered substances. Disruptions to this barrier, such as dryness or irritation, lead to higher TEWL and greater skin sensitivity, illustrating how central permeability control is to skin health. UV protection exists as well, due to melanin and UV-absorbing compounds, but that function is separate from the barrier’s permeability role. Temperature regulation involves sweat and blood flow, not the barrier per se. And while the barrier reduces water loss, it does not prevent all water loss—some normal TEWL always occurs. So, describing the skin as acting as a permeability barrier best captures the true function being tested.

The main idea tested is what the skin’s barrier function actually does. The skin’s barrier is best described as a permeability barrier: the outermost layer, the stratum corneum, forms a tight, lipid-rich shield that limits the diffusion of water and chemicals into the body and helps keep internal fluids from evaporating away. This brick-and-mortar arrangement—corneocytes as “bricks” and lipids (ceramides, cholesterol, free fatty acids) as the “mortar”—creates the hydrophobic environment that reduces transepidermal water loss (TEWL) and blocks many externally encountered substances.

Disruptions to this barrier, such as dryness or irritation, lead to higher TEWL and greater skin sensitivity, illustrating how central permeability control is to skin health. UV protection exists as well, due to melanin and UV-absorbing compounds, but that function is separate from the barrier’s permeability role. Temperature regulation involves sweat and blood flow, not the barrier per se. And while the barrier reduces water loss, it does not prevent all water loss—some normal TEWL always occurs.

So, describing the skin as acting as a permeability barrier best captures the true function being tested.