If a patient presents with a painful, warm, swollen red lump on the eyelid, what is the most likely diagnosis?

The presentation of a painful, warm, swollen red lump on the eyelid is most characteristic of a hordeolum, commonly known as a stye. A hordeolum typically arises from the infection of the sebaceous glands located at the base of the eyelashes (usually caused by Staphylococcus bacteria) or from the blockage of these glands.

The key features supporting this diagnosis include the localized pain, warmth, and redness, which are indicative of an acute inflammatory response associated with infection. The lump itself represents an abscess formation that can occur due to the clogging and bacterial infection of these glands.

In contrast, while a chalazion can also present as a lump on the eyelid, it is usually not painful and occurs due to blockage and inflammation of meibomian glands, often resulting in a painless lump. Dacryocystitis involves inflammation of the tear sac, typically presenting with tearing and redness around the area of the tear duct, rather than a localized lump on the eyelid itself. Blepharitis, which is an inflammation of the eyelid margins, usually presents with irritation, crusting, or scaling and does not typically manifest as a singular painful lump.

Thus, the specific characteristics of