**Core Concept**
Lichenisation is a characteristic skin change seen in chronic inflammatory conditions, such as eczema or psoriasis. It involves a thickening of the epidermis, leading to a rough, leathery texture. This process is mediated by the keratinocyte proliferation and increased expression of adhesion molecules.

**Why the Correct Answer is Right**
In lichenisation, there is a marked increase in the thickness of the stratum corneum, which is the outermost layer of the epidermis. This thickening is due to the increased proliferation of keratinocytes, which are the primary cell type in the epidermis. The stratum corneum is composed of dead, flattened keratinocytes that provide a barrier against water loss and external pathogens. The increased expression of adhesion molecules, such as E-cadherin, also plays a role in the process of lichenisation by promoting the adhesion of keratinocytes to each other.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because lichenisation primarily affects the epidermis, not the dermis. The dermis is the layer of skin beneath the epidermis, and it is not directly involved in the process of lichenisation.
* **Option B:** This option is incorrect because lichenisation is not a characteristic of the stratum basale, which is the innermost layer of the epidermis. The stratum basale is composed of a single layer of columnar or cuboidal keratinocytes that are attached to the dermis via hemidesmosomes.

**Clinical Pearl / High-Yield Fact**
Lichenisation is a common skin change seen in chronic inflammatory conditions, and it can be a useful diagnostic clue in patients with a history of eczema, psoriasis, or other skin disorders. It is also associated with an increased risk of skin cancer, particularly squamous cell carcinoma.

**Correct Answer: C. Stratum corneum. The stratum corneum is the outermost layer of the epidermis, and it is primarily affected in lichenisation.**