Recently I have been reading a lot about Momento Mori and the Black Plague.  Macabre, I know!  But it is just so interesting.  What is even more interesting is the Plague Doctor's wardrobe and it's purpose.  Here is a description from wikipedia:
"A plague doctor's duties were often limited to visiting victims to verify whether they had been afflicted or not. Surviving records of contracts drawn up between cities and plague doctors often gave the plague doctor enormous latitude and heavy financial compensation, given the risk of death involved for the plague doctor himself. Most plague doctors were essentially volunteers, as qualified doctors had (usually) already fled, knowing they could do nothing for those affected.

Considered an early form of hazmat suit, a plague doctor's clothing consisted of:

  • A wide-brimmed black hat worn close to the head. At the time, a wide-brimmed black hat would have identified a person as a doctor, much the same as how nowadays a hat may identify chefs, soldiers, and workers. The wide-brimmed hat may have also been used as partial shielding from infection.
  • A primitive gas mask in the shape of a bird's beak. A common belief at the time was that the plague was spread by "bad air". There may have been a belief that by dressing in a bird-like mask, the wearer could draw the plague away from the patient and onto the garment the plague doctor wore. The mask also included red glass eyepieces, which were thought to make the wearer impervious to evil. The beak of the mask was often filled with strongly aromatic herbs and spices to overpower the miasmas or "bad air" which was also thought to carry the plague. At the very least, it may have dulled the smell of unburied corpses, sputum, and ruptured bouboules in plague victims.
  • A long, black overcoat. The overcoat worn by the plague doctor was tucked in behind the beak mask at the neckline to minimize skin exposure. It extended to the feet, and was often coated head to toe insuet or wax. A coating of suet may have been used with the thought that the plague could be drawn away from the flesh of the infected victim and either trapped by the suet, or repelled by the wax. The coating of wax likely served as protection against respiratory droplet contamination, but it was not known at the time if coughing carried the plague. It was likely that the overcoat was waxed to simply prevent sputum or other bodily fluids from clinging to it.
  • A wooden cane. The cane was used to both direct family members to move the patient, other individuals nearby, and possibly to examine patients without directly touching them.
  • Leather breeches. Similar to waders worn by fishermen, leather breeches were worn beneath the cloak to protect the legs and groin from infection. Since the plague often tended to manifest itself first in the lymph nodes, particular attention was paid to protecting the armpits, neck, and groin.
It is not known how often or widespread plague doctors were, or how effective they were in treatment of the disease. It's likely that while the plague doctor's clothing offered some protection to the wearer, the plague doctors themselves may have actually contributed more to the spreading of the disease than its treatment, in that the plague doctor unknowingly served as a vector for infected fleas to move from host to host."

And what is even better, is Fever Ray's use of masks and disguises whenever they make public appearances.. So intriguing!