**Core Concept**
Essential fatty acid deficiency (EFAD) arises when the body lacks adequate intake of linoleic acid (omega-6) and α-linolenic acid (omega-3), which are critical for membrane integrity, inflammation regulation, and skin health. In long-term parenteral nutrition, especially with absence of dietary fats, EFAD can develop due to insufficient fat supplementation.

**Why the Correct Answer is Right**
EFAD manifests clinically with dry, scaly skin, alopecia (hair loss), and eczema-like dermatitis due to impaired skin barrier function and lipid metabolism. These signs are typically seen in prolonged parenteral nutrition without fat infusion. The deficiency is not due to frequency of fat administration but rather total fat deficiency. Soybean oil, rich in linoleic acid, must be provided regularly (daily) to prevent EFAD, not just weekly. Thus, option C accurately describes the classic clinical presentation.

**Why Each Wrong Option is Incorrect**
Option A: Soybean oil given only once weekly is insufficient to prevent EFAD; essential fatty acids require continuous intake to maintain tissue levels.
Option B: EFAD is not usually noted at the end of the first week; it develops over days to weeks due to cumulative fat deficiency.
Option D: EFAD is associated with **hypolipidemia**, not hypercholesterolemia; cholesterol levels typically decrease, not increase.

**Clinical Pearl / High-Yield Fact**
In patients on long-term parenteral nutrition, essential fatty acid deficiency leads to dermatological signs like dry, scaly skin and hair loss. Always include a fat source (e.g., soybean oil) in the formula to prevent this deficiency.

✓ Correct Answer: C. It causes dry scaly skin with loss of hair.