Bloodshot eyes are often caused by dilated capillaries in the eyes, such as wearing contact lenses to bed, which can lead to a lack of oxygen in the eyes, which in turn can lead to bloodshot eyes. In addition, excessive fatigue, staying up late, and poor eye habits can all lead to bloodshot eyes. Blood in the eyes may also be caused by pathological factors such as conjunctivitis, uveitis, glaucoma, keratitis, etc.: 1. Conjunctivitis: Common infectious conjunctivitis includes bacterial conjunctivitis, viral conjunctivitis, trachoma, etc. Patients usually present with conjunctival congestion, blood, and increased eye discharge. Common non-infectious conjunctivitis is mainly allergic conjunctivitis, caused by external allergens, such as exposure to pollen, willow, dust and other allergens, which stimulate allergic reactions in the conjunctiva, resulting in eye congestion, blood and dry itching. 2. Glaucoma: It is caused by congenital or acquired causes that block the circulation of atrial fluid in the eye, thus triggering an increase in intraocular pressure and resulting in damage to the optic nerve. Patients show symptoms such as eye congestion, blood, vision loss, eye swelling and pain, nausea, vomiting, etc. 4, keratitis: mainly includes bacterial keratitis, viral keratitis and fungal keratitis, etc. Patients usually show symptoms such as eye congestion, blood, eye pain and vision loss, etc. 5, sclerenitis: refers to inflammation of the sclera, patients show blood in the sclera, accompanied by Other causes: For example, dry eye, patients often have dryness, itchiness, foreign body sensation, and blood in the conjunctiva. In addition, when a foreign body enters the eye surface, it may cause the patient’s eyes to become congested with a strong foreign body sensation.