Some types are contagious and some types are not. The conjunctiva is a soft, smooth and clear membrane located on the inner surface of the eyelid and the surface of the eye. Conjunctivitis is a common and prevalent clinical condition. To determine if conjunctivitis is contagious, it is important to first identify the cause of the disease and what is causing the conjunctivitis. The etiology of conjunctivitis can be divided into two categories, infectious and non-infectious, depending on its different nature. 1. Infectious: inflammation of the conjunctiva due to infection by pathogenic microorganisms. Non-infectious: allergic inflammation caused by local or systemic allergic reactions is the most common. External physical and chemical factors such as light and various chemicals can also be causative factors. General infectious conjunctivitis, which is contagious, includes bacterial conjunctivitis, viral conjunctivitis, and chlamydial conjunctivitis, or trachoma, which is transmitted by contact, and the main way to block the infection is to wash hands and not to share towels with patients. Allergic conjunctivitis caused by pollen, dust, animal hair, dust mites, etc. is not contagious. Therefore, there are many types of conjunctivitis, but not all of them are contagious, but some are.