Folliculitis: A small, transient inflammatory nodule on the scalp is most likely folliculitis, an inflammation of the hair follicle often caused by bacterial or fungal infections. This condition is common and can be related to acne or pimples, especially if the scalp is prone to oiliness.

Seborrheic Dermatitis: While seborrheic dermatitis typically presents as a diffuse, scaly eruption, it can sometimes manifest as smaller, inflamed nodules, especially in the scalp area. The condition is associated with an oily scalp and can be itchy.
Acne Keloidalis Nuchae (AKN): AKN is a type of acne that occurs on the back of the neck and scalp, characterized by inflamed papules and pustules that can form keloid-like scars. It's more common in individuals with curly hair and can be exacerbated by friction and ingrown hairs.
Pilar Cyst: A pilar cyst, also known as a trichilemmal cyst, is a benign cyst that originates from the hair follicle. While it's usually not inflammatory, it can become inflamed and present as a red nodule if infected.

Keratoacanthoma: Although rare, keratoacanthoma is a low-grade malignancy that can present as a rapidly growing, inflamed nodule. It's crucial to distinguish it from other benign conditions due to its potential for local destruction and rare metastatic potential.
Squamous Cell Carcinoma: This is a type of skin cancer that can present as a firm, growing nodule. While less common on the scalp compared to sun-exposed areas, it's a critical diagnosis not to miss due to its potential for metastasis.
Basal Cell Carcinoma: The most common form of skin cancer, basal cell carcinoma can appear as a small, shiny bump on the scalp. It's usually slow-growing but can be locally destructive if left untreated.

Angiolymphoid Hyperplasia with Eosinophilia (ALHE): A rare condition characterized by the growth of blood vessels and the presence of eosinophils, leading to inflamed nodules. It's more common in the head and neck area.
Eosinophilic Pustular Folliculitis (EPF): A rare skin condition that presents with itchy, pus-filled bumps, particularly on the scalp. It's associated with an eosinophilic infiltrate and can be challenging to diagnose.
Langerhans Cell Histiocytosis (LCH): A rare disorder in which the body accumulates too many immature Langerhans cells, part of the immune system. It can present with skin lesions, including on the scalp, among other systemic symptoms.