A swollen upper eyelid is often caused by a common eye problem such as a stye, blepharitis, conjunctivitis, allergy, or irritation from products used around the eyes. It may look puffy, red, sore, itchy, or feel tender, depending on the cause.
A stye usually causes a small, painful lump on the eyelid, while blepharitis tends to cause swollen, irritated eyelid edges with crusting near the lashes. Conjunctivitis can also make the eyelids very swollen, usually along with eye redness, watering, discharge, or a gritty feeling.
Sometimes swelling is linked to contact dermatitis from cosmetics, eye drops, nail products, or skin products that touch the eyelids. More serious causes, such as periorbital cellulitis or orbital inflammation, are more likely when swelling is one-sided, painful, spreading, or linked to fever, vision changes, or trouble moving the eye.
Avoid self-medicating, especially with leftover antibiotics, steroid drops, or creams near the eye. If the swelling is severe, painful, keeps coming back, affects vision, or does not improve, it is best to see an ophthalmologist.