**Core Concept**
Glucocorticoids, such as cortisol, have a wide range of effects on the skin and connective tissue, primarily mediated through their interaction with the glucocorticoid receptor. This interaction triggers a cascade of intracellular signaling events that ultimately influence various cellular processes.

**Why the Correct Answer is Right**
Cortisol exerts antiproliferative effects on fibroblasts and keratinocytes by inhibiting the expression of genes involved in cell growth and proliferation. This action leads to a decrease in the production of collagen and other extracellular matrix components, resulting in loss of collagen and atrophy of the skin. Hyperpigmentation, on the other hand, is typically associated with increased melanocyte-stimulating hormone (MSH) activity, which is not directly influenced by cortisol. Instead, cortisol causes a redistribution of melanin, leading to a decrease in skin pigmentation.

**Why Each Wrong Option is Incorrect**
**Option A:** Cortisol indeed has an antiproliferative effect on fibroblasts, which contributes to the atrophy of skin and connective tissue.
**Option B:** Similarly, cortisol also exerts an antiproliferative effect on keratinocytes, leading to a decrease in skin thickness.
**Option C:** The loss of collagen is a direct consequence of cortisol's antiproliferative effect on fibroblasts and its inhibition of collagen synthesis.

**Clinical Pearl / High-Yield Fact**
Cortisol's effects on the skin and connective tissue are a classic example of a glucocorticoid-induced atrophy, which can be reversed upon withdrawal of the steroid. This is a critical consideration in the management of patients on long-term glucocorticoid therapy.

**✓ Correct Answer: D. Hyperpigmentation.**