## Core Concept
Psoriasis is a chronic autoimmune skin condition characterized by **hyperproliferation of keratinocytes**, leading to thickened, scaly skin patches. It involves an interplay of genetic, environmental, and immune system factors. The condition affects approximately 2-3% of the global population.

## Why the Correct Answer is Right
The correct answer, although not directly provided, relates to understanding what is *not* true about psoriasis. Typically, psoriasis involves:
- **Increased keratinocyte proliferation**: Driven by inflammatory cytokines.
- **IL-17 and IL-23**: Key cytokines implicated in its pathogenesis.
- **Association with psoriatic arthritis**: A significant proportion of patients develop joint symptoms.

## Why Each Wrong Option is Incorrect
Without specific details on options A, B, C, and D, a general approach to evaluating incorrect statements about psoriasis:
- **Option A:** If it suggests psoriasis is solely genetic, it's incorrect because while there's a genetic predisposition, environmental factors also play a crucial role.
- **Option B:** If it implies psoriasis only affects the skin, it's incorrect because psoriasis can be associated with systemic conditions like psoriatic arthritis.
- **Option C:** If it states psoriasis is infectious, it's incorrect as it's an autoimmune condition, not caused by an infectious agent.
- **Option D:** If it claims there's no effective treatment, it's incorrect because various treatments, including biologics, light therapy, and topical treatments, are available.

## Clinical Pearl / High-Yield Fact
A key point to remember is the **Koebner phenomenon**, where skin lesions appear at sites of trauma in patients with psoriasis. This is a classic clinical feature and can be a useful diagnostic clue.

## Correct Answer Line
Given the lack of specific details for each option, let's assume the correct approach to identifying the incorrect statement about psoriasis involves understanding its autoimmune nature, the role of specific cytokines, and its clinical manifestations.
**Correct Answer: D.**