Seborrheic Dermatitis: This condition is characterized by a red, itchy, and flaky scalp, often associated with oily skin. It's a common condition in young adults, making it the most likely diagnosis given the patient's age and symptoms.

Dandruff: A mild form of seborrheic dermatitis, dandruff causes flakes on the scalp and can be itchy. It's very common and can be treated with over-the-counter shampoos.
Psoriasis: An autoimmune condition that can cause red, itchy patches on the scalp. It's less common than seborrheic dermatatitis but still a likely consideration.
Contact Dermatitis: An allergic reaction or irritation from hair products can cause a red and itchy scalp. Given the wide use of hair care products, this is a plausible diagnosis.
Tinea Capitis (Ringworm of the Scalp): A fungal infection that can cause redness, itching, and hair loss. It's more common in children but can occur in adults.

Scalp Cellulitis or Abscess: Bacterial infections that can cause redness, swelling, and pain on the scalp. These conditions require prompt antibiotic treatment and can be serious if not addressed.
Malignancy (e.g., Cutaneous T-Cell Lymphoma): Although rare, certain types of skin cancer can present with itching and redness on the scalp. Early detection is crucial for effective treatment.

Kerion: A severe form of tinea capitis that can cause significant inflammation and pus on the scalp. It's rare but can occur, especially in immunocompromised individuals.
Pityriasis Amiantacea: A condition characterized by thick, yellow scales on the scalp, often associated with psoriasis. It's less common and might be considered if other treatments fail.
Lichen Planopilaris: An autoimmune condition that can cause itching, redness, and hair loss on the scalp. It's rare and might be considered if other diagnoses are ruled out.