## **Core Concept**
The question pertains to the adverse effects of topical corticosteroids, which are commonly used for treating various skin conditions due to their anti-inflammatory and immunosuppressive properties. The complications of topical corticosteroids can range from local to systemic effects, depending on the potency of the steroid, the duration of use, and the area of application.

## **Why the Correct Answer is Right**
The correct answer, **C. Skin atrophy**, is a well-known complication of long-term topical corticosteroid use. Skin atrophy results from the thinning of the skin due to the reduction in the thickness of the epidermis and dermis. This occurs because corticosteroids inhibit the synthesis of collagen and other matrix components, leading to a decrease in dermal thickness. Skin atrophy is a common and significant side effect that can make the skin more susceptible to damage and tearing.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While systemic absorption of topical corticosteroids can lead to systemic effects similar to those of Cushing's syndrome, this is not the most common complication, especially with topical use.
- **Option B:** Striae (stretch marks) are indeed a complication of topical corticosteroid use, but they are not as universally common or directly associated with prolonged use as skin atrophy.
- **Option D:** Allergic dermatitis or contact dermatitis can occur with many topical medications, including corticosteroids, but it is not the most common complication directly attributable to the use of topical corticosteroids themselves.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the risk of skin atrophy with topical corticosteroids increases with the potency of the corticosteroid and the duration of its use. Therefore, it's crucial to use these medications judiciously and consider less potent alternatives or intermittent therapy to minimize side effects.

## **Correct Answer:** C. Skin atrophy