Angular Cheilitis: This condition is characterized by inflammation of the corners of the mouth and can lead to the formation of thick, black scabs on the lips due to fungal or bacterial infections. It's a common issue, especially in individuals with poor oral hygiene, nutritional deficiencies, or those who wear dentures.

Cold Sore (Herpes Simplex Virus): Although typically presenting with clear vesicles that crust over, in some cases, especially if secondarily infected, cold sores can appear as thick, black scabs on the lips.
Impetigo: A highly contagious bacterial skin infection that can cause black scabs, especially if the infection is deep or if the individual picks at the sores.
Eczema (Atopic Dermatitis): In severe cases, eczema on the lips can lead to thickening of the skin and formation of scabs, which might appear black due to dried blood or melanin accumulation.

Squamous Cell Carcinoma: Although less common, this type of skin cancer can present as a non-healing sore or scab on the lip. It's crucial to consider this diagnosis, especially in individuals with a history of sun exposure or tobacco use.
Methamphetamine Use: Methamphetamine users can develop a condition known as "meth mouth," which includes severe dental and oral health issues, potentially leading to black scabs on the lips due to poor oral health and malnutrition.

Mucous Membrane Pemphigoid: An autoimmune disease that can cause blistering of the mucous membranes, including those on the lips, potentially leading to scabbing.
Discoid Lupus Erythematosus: A chronic skin condition of sores with inflammation and scarring favoring the face, ears, and scalp but can also affect the lips, leading to scabbing.
Actinic Cheilitis: A condition caused by prolonged exposure to the sun, leading to inflammation of the lips, which can result in scabbing and has the potential to develop into squamous cell carcinoma.