In 1948, she teamed up with Rachel Fuller Brown to develop nystatin, the first non-toxic drug treatment for fungal infections in humans.

Her research had multiple applications ranging from saving infected trees to restoring paintings and artwork damaged due to mold.

Following her teaching job, Hazen applied and was accepted into the Department of Biology at Columbia for graduate studies.

[4] In the 1920s, while studying at Columbia University, Hazen worked with ricin and its effect on Clostridium botulinum toxin.

From there, she worked at the New York office of the Division of Laboratories and Research of the State Department of Public Health.

In 1944, she was chosen by Augustus Wadsworth, founder and head of the division, to be in charge of an investigation into fungi and their relation to bacteria and other microbes.

This included diseases such as pneumonia and moniliasis (thrush), a mouth condition that makes swallowing painful.

Dr. Hazen cultured Actinomycetes (microorganisms most frequently having antifungal properties) from each sample and tested them to see if any fungal activity was present.

[8] They originally named it fungicidin, but later renamed it nystatin, in honor of their employer, the New York State Department of Public Health.

[6][9] In fall 1950, Dr. Hazen and Dr. Brown announced at a National Academy of Sciences meeting that they had successfully produced two antifungal agents from an antibiotic.

This led to their development of nystatin (named in honor of the New York State Public Health Department), the first fungicide safe for treating humans.

It took Hazen, Brown, and Squibb Research Company six and half years to secure a patent for the invention.