The pins and needles sensation on the left side of the face may be caused by trigeminal neuralgia, mosquito bites, allergic dermatitis and other reasons. 1. Trigeminal neuralgia: it may be caused by thickening of meninges, compression of semilunar ganglion, meningitis and so on. The pain that patients experience often starts from the maxillary or mandibular branch on one side of the face, and the phenomenon of pins and needles on the left side of the face may appear in the early stage. 2. Mosquito bites: If the left side of the patient’s face is bitten after contact with mosquitoes and caterpillars, an inflammatory reaction may occur, causing redness and swelling. Serious patients may have a pinprick sensation. 3. Allergic dermatitis: may be due to the left side of the face in contact with skin care products, with irritating ingredients appear allergic. The patient may have a pins and needles sensation on the left side of the face, which may be accompanied by an itching sensation. It is recommended that patients with pins and needles on the left side of the face go to the hospital in a timely manner and follow the doctor’s instructions for treatment to avoid delaying the condition.