**Comedones are seen in Open Comedones (Blackheads) and Closed Comedones (Whiteheads)**

**Core Concept**
Comedones are a type of acne lesion characterized by the accumulation of sebum and dead skin cells within the pilosebaceous unit. They are a result of the obstruction of the sebaceous follicle, leading to the formation of either open comedones (blackheads) or closed comedones (whiteheads).

**Why the Correct Answer is Right**
The formation of comedones is primarily due to the hyperkeratosis and hyperseborrhoea of the pilosebaceous unit. The obstruction of the sebaceous follicle is caused by the overproduction of sebum and the accumulation of dead skin cells. This leads to the formation of a keratin plug, which traps the sebum and bacteria within the follicle, resulting in the characteristic appearance of comedones. The bacteria present in the comedone contribute to the inflammatory response, leading to the development of acne.

**Why Each Wrong Option is Incorrect**
**Option A:** Sebaceous cysts are a different type of skin lesion that results from the obstruction of the sebaceous gland, but they do not form comedones.
**Option B:** Erythema nodosum is a type of skin inflammation that presents as red, painful nodules, but it is not related to the formation of comedones.
**Option C:** Folliculitis is an inflammation of the hair follicle, but it is not the same as the formation of comedones.

**Clinical Pearl / High-Yield Fact**
Comedones are often associated with acne vulgaris, but they can also occur in other conditions such as seborrhoeic dermatitis and rosacea.

**Correct Answer: C. Comedones are seen in Open Comedones (Blackheads) and Closed Comedones (Whiteheads).**