Sick people and postpartum women who are liable to catch a cold if they walk barefoot on the ground may wear leather shoes (SA 614:3).
One who is walking in an area where there is concern for scorpions and the like may wear leather shoes. Likewise, one who is walking in a muddy place may wear his regular shoes to avoid soiling his feet. A soldier on active duty may wear army boots (SA 614:4). The reason for these leniencies is that wearing shoes is prohibited only if one wears them for the sake of comfortable walking. When there is different reason for wearing them, however, the prohibition does not apply.
One who needs orthotic shoe inserts and suffers greatly without them may insert them into slippers or thin rubber shoes and use them on Yom Kippur, because orthotics are not worn for pleasure, but to alleviate terrible pain (Ḥelkat Ya’akov 2:83).