## Core Concept
The thickness of a split skin graft refers to the proportion of the dermis that is included in the graft. Split skin grafts, also known as partial-thickness skin grafts, include the epidermis and a variable portion of the dermis. The thickness of the graft affects its properties, such as vascularization, strength, and cosmetic outcome.

## Why the Correct Answer is Right
As the thickness of a split skin graft increases, it includes more of the dermis. This has several implications:
- **Vascularization:** Thicker grafts have a more extensive dermal plexus, which can lead to better initial vascularization and graft take.
- **Strength and Durability:** The dermis provides much of the skin's strength. Therefore, thicker grafts are stronger and less prone to injury.
- **Cosmetic Outcome:** Thicker grafts tend to have a better cosmetic outcome because they more closely resemble the normal skin architecture.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because as the graft thickness increases, the donor site's ability to regenerate epithelial cells from adnexal structures (like hair follicles and sweat glands) might be less affected, but the primary concern is the graft's properties.
- **Option B:** This option is incorrect because while it's true that very thin grafts have a higher risk of contraction, the relationship between graft thickness and contraction is more complex and involves the amount of dermis included.
- **Option C:** This option might seem plausible because thicker grafts do have a better cosmetic outcome due to their more normal architecture, but the question specifically asks about the increase in thickness.

## Clinical Pearl / High-Yield Fact
A key point to remember is that as the thickness of a split skin graft increases, so does its resistance to contraction. This is clinically significant because contraction can affect the functional and cosmetic outcome of the graft, especially over joints or on the face.

## Correct Answer: C.