Conjunctivitis can cause eyelid swelling because it is caused by an inflammatory infection of the conjunctiva, lid conjunctiva, or bulbar conjunctiva of the eyelid, causing swelling, congestion, or increased secretions, which can lead to edema under the skin of the eyelid, also known as swelling. Conjunctivitis is classified as acute, subacute, or hyperacute. In particular, hyperacute acute conjunctivitis causes more eyelid swelling because it causes an acute edematous reaction in the lid conjunctiva, and the connective tissue under the skin of the eyelid also swells, along with edema, so that the eyelid looks swollen and higher. However, there are some chronic conjunctivitis that usually do not have eyelid swelling, such as mild trachoma and chronic conjunctivitis.