Trigeminal Neuralgia: This condition is characterized by sudden, severe, and stabbing pain or numbness in parts of the face, which can be triggered by light touch. It often affects one side of the face, making it a plausible explanation for left facial numbness.

Multiple Sclerosis (MS): MS is an autoimmune disease that can cause numbness or tingling in the face, among other symptoms. The numbness can be unilateral and is a common presenting symptom.
Stroke or Transient Ischemic Attack (TIA): Although more commonly associated with motor deficits, strokes or TIAs can cause numbness or sensory changes, including facial numbness.
Migraine: Some types of migraines can cause numbness or tingling sensations in the face, which may precede or accompany the headache.

Lyme Disease: Caused by the bacterium Borrelia burgdorferi, Lyme disease can lead to neurological manifestations, including facial numbness or palsy, especially if left untreated.
Sarcoidosis: This inflammatory disease can affect various parts of the body, including the nervous system, leading to facial numbness among other symptoms.
Brain Tumors: Tumors in the brain, depending on their location, can cause a variety of symptoms, including facial numbness. Early detection is crucial for treatment and prognosis.

Sjögren's Syndrome: An autoimmune disorder that primarily affects the glands that produce tears and saliva but can also have neurological manifestations, including facial numbness.
Vitamin Deficiencies (e.g., Vitamin B12 Deficiency): Certain vitamin deficiencies can lead to neurological symptoms, including numbness or tingling in the face, although this is less common.
Peripheral Neuropathy: While more commonly associated with symptoms in the hands and feet, certain types of peripheral neuropathy can cause facial numbness, especially if the trigeminal nerve is involved.