The most common cause of proptosis in adults:-
Orbital cellulitis
Preseptal cellulitis
Thyroid eye disease
Capillary hemangioma
Most common cause of unilateral proptosis in children is orbital cellulitis and in adults is thyroid ophthalmopathy. Most common cause of bilateral proptosis in children is neuroblastoma and leukemia (chloroma) and in adults is thyroid ophthalmopathy.
NEET 2019