Itchy eyes are one of the common clinical symptoms of ophthalmology, and there are many causes of itchy eyes. The most common causes are: (1) Immune conjunctivitis: a hypersensitive immune response of the conjunctiva to external allergens. The conjunctiva is often exposed to airborne allergens such as pollen, dust, animal fur, cockroaches, trees, and grass, and is also susceptible to bacterial or other microbial infections and allergies resulting in immune conjunctivitis. Some of them are caused by long-term topical use of eye drops such as antibiotics, surface anesthetics, atropine, trichothecene, and sulfonamides that lead to medical conjunctival contact or allergic conjunctivitis. These eye diseases have eye itching in common, and some are even unbearably itchy. (2) Contact dermatitis: eyelid skin contact with cosmetics, thin and tender eyelid skin, rich in blood vessels, is more sensitive to cosmetic stimulation, and some people may have serious allergic reactions to their eyelids even though they are only exposed to a small amount of cosmetics. Or water running onto the eyelid skin when washing hair after dyeing can cause diffuse skin tension on the eyelid, with little skin temperature and no tenderness, but an itchy sensation. Head oil is most likely to cause allergy and is long and symptomatic. The above eyelid skin itch is collectively referred to as contact dermatitis. (3) Blepharitis: Blepharitis is one of the common clinical eye diseases associated with fine infection, physical and chemical irritation, refractive error, chronic conjunctivitis, overflowing tears, cryptopia, poor hygiene habits and decreased body resistance. Itching, burning and irritation of the lid margins, flushing, congestion, hypertrophy, seborrhea, crusting and scaling after drying, and easy loss of eyelashes. (4) Chronic bacterial conjunctivitis: Chronic bacterial conjunctivitis can evolve from acute conjunctivitis or be caused by less virulent pathogenic bacteria. There are chronic lacrimal sacculitis, lacrimal duct obstruction, lid gland insufficiency, etc. can be caused. Itching in one or both eyes, burning sensation, eye stinging, dryness and discomfort, easy fatigue. There is increased mucus secretion or white vesicles in the corners of the eyes and crusting of the skin at the canthus. The disease progresses slowly and lasts for a long time. (5) Lid gland dysfunction: associated with Staphylococcus epidermidis, Corynebacterium and Propionibacterium acnes infections. There is often redness, itching, dryness, photophobia, tearing, burning sensation, foreign body sensation, fluctuating vision, and visual fatigue. The lid margins are congested, irregular, thickened, with blunt posterior margins and scaly eyelash roots; the lid gland orifice is prominent, displaced, with indistinct borders, dilated surrounding capillaries, obstructed by yellow lipid secretions, and yellowish-white, or granular, or toothpaste-like secretions spill from the lid gland opening when the lid margin is squeezed. (6) Trachoma: Trachoma is a contagious conjunctival keratitis caused by Chlamydia trachomatis infection. The symptoms in the acute phase are mainly photophobia, lacrimation, foreign body sensation, and more mucus or mucopurulent discharge. In the chronic phase, the main symptoms are itching, foreign body sensation, dryness and discomfort, and burning sensation in both eyes. Trachoma was a widespread eye disease in China in the 1950s and was the leading cause of blindness at that time. After the 1970s, with the improvement of living standards, health knowledge and medical conditions, its incidence has been greatly reduced, but it is still a common conjunctival disease. The prevalence of trachoma in many areas of China is still as high as 20% or more. Trachoma infection can last for several years or even decades, and can cause blindness in severe cases. Trachoma is currently one of the major eye diseases causing blindness in China. Despite the leap forward in medical science, the understanding of itch is still inadequate. Pain, touch, temperature and itch can be felt by the corresponding nerve tissue on the skin surface, but the itch receptor has not been confirmed so far. Some people believe that itch is caused by a slight stimulation of nociceptive receptors. It is believed that itch is a “low pain” sensation, the skin of nociceptive dull, normal pain stimulation only cause itching, nociceptive sensitive skin, “low pain” stimulation can cause itching; no nociceptive skin, such as leprosy patients have neither pain nor itch. After a skin injury, as long as the nociceptive transmission pathway is still present, it will itch once the wound is almost healed. In addition, some people believe that itch is a completely independent sensation, reasoning that even intense itch cannot be converted into pain, itch and pain can coexist, scratching can stop itch but not pain, morphine can stop pain but cause itchiness. By removing the epidermis and subepidermal nerve plexus, no itching occurs and the pain remains. It is now accepted that the various impulses from the skin are collected by nerve fibers in the spinal cord and higher nerve centers and then transmitted to the cerebral cortex for analysis, and if the sensory information transmitted by the nerves is incomplete or unclear, this is the itch sensation. Regarding the neurotransmission pathway of itch, it is generally believed that the itch receptors, transmit the itch sensation along the spinal nerve fibers to the spinal cord, then to the thalamus, and from the thalamus to an area of the cerebral cortex. This neurotransmission pathway happens to be the transmission pathway of nociception, so it can explain that when the skin of the eye itches, the pain sensation caused by scratching replaces the itch sensation and acts as an antipruritic agent.