Don Milton, MD, DrPH
Professor of Environmental Health, Applied Environmental Health (MIAEH)
Affiliate in Cell Biology and Molecular Genetics; Professor, Internal Medicine, University of Maryland School of Medicine
Other Affiliations: UMD Prevention Research Center
Campus: UMD | Building: School of Public Health | Room: 2234V
Phone: 301-405-0389 | |
Laboratory Website: 
Public Health Aerobiology, Virology, and Exhaled Biomarker Laboratory (PHAB Lab)
Stop COVID Study
Office Hours: 

By appointment


Dr. Donald K. Milton is a pioneer of the modern science of airborne transmission of respiratory viruses. Starting in the late 1990s, he proposed that monitoring carbon dioxide concentrations indoors could be used as a marker for risk of respiratory virus transmission. The idea initially met with derision. His original paper demonstrating a mathematical model illustrating the concept was rejected at Science and other journals before being published by Indoor Air in 2003. He supported this concept with epidemiologic studies published in several journals between 1998 and 2004. 

Today, his idea has gained wide acceptance and is now promoted by many scientists and public health experts as a means of identifying high risk environments for the spread of COVID-19. His work also provided a key piece of the scientific basis for masks mandates that are now common throughout the world including the publication of a key paper April 1, 2020 that was downloaded over two million times during the first year of the pandemic. Together these contributions by Milton provide key elements of the scientific foundation for the two most effective non-pharmaceutical interventions being deployed to control the SARS-CoV-2 pandemic. In recognition of his contributions, he has been asked by his scientific colleagues to take a leading role in efforts to persuade the WHO and CDC to fully acknowledge the importance of aerosols and their control in protecting essential workers and the public.

Milton’s work supporting the mask mandate started with his work on exhaled breath aerosols. He led development of two novel exhaled breath samplers (G-II, patent no. US 8,250,903, and the IcePac patent no. US 10,502,655). These instruments are unique in that they allow collection of exhaled breath aerosols while preserving biological properties including the infectiousness of viral aerosols. The G-II allows collection while a subject breathes normally, coughs spontaneously, and talks, sings or wears a face mask. Using the G-II, he and colleagues demonstrated that breath contains infectious influenza virus (not merely viral RNA), quantified the rate of aerosol shedding of both viral RNA and infectious influenza virus, and demonstrated the impact of face masks on influenza aerosol shedding published in PLoS Path (2013) and PNAS (2018). He then supervised a doctoral student in Hong Kong whose work using a G-II sampler showed that face masks block aerosol shedding of seasonal coronaviruses (Leung et al. Nat. Med. 2020).

This work was cited by the National Academies in an April 1, 2020 letter to the White House as key evidence that face masks would make important contributions to controlling spread of COVID-19. In less than a year since publication, the paper has received significant attention with many citations (490 Scopus, 1039 Google Scholar, 198 Web of Science) and public and media attention (2.09 million downloads, Almetric score 20,848, 40,70 tweeters, 717 news outlets, 112 blogs, 69 Facebook pages and 22, video uploaders) making it the 6 th highest ranked paper for online attention of 27,7972 papers tracked by Atmetric. Milton is currently leading an NIH-, CDC-, and Bill and Melinda Gates Foundation- funded project focused on quantifying infectious exhaled aerosols from COVID-19 cases using the G-II and IcePac samplers and to examine the impact of face masks on SARS-CoV-2 shedding. His Public Health Aerobiology and Biomarkers (PHAB) Laboratory team is routinely performing assays for SARS-CoV-2 clinical specimens (saliva, swabs, exhaled breath) and environmental samples using the Thermo TaqPath® assay and multiple respiratory pathogens using TaqMan Array Card® assays.

Donald K. Milton, MD, DrPH is Professor of Environmental Health, School of Public Health, with a secondary appointment as Professor in the Department of Medicine, School of Medicine. He earned a BS in Chemistry from UMBC, MD from Johns Hopkins, and an MOH and a DrPH (Environmental Health) from Harvard. He is a Diplomat of the American Boards of Internal and Preventive (Occupational) Medicine and a Fellow of the International Society for Indoor Air Quality and Climate. He has served on the editorial boards of Applied Environmental Microbiology, Indoor Air, and BMC Public Health, and on the NIOSH NORA Indoor Environment Team and chaired the ACGIH Bioaerosols Committee. 

Professional Interests:

Milton’s work focuses on the interrelated areas of infectious bioaerosols, exhaled breath analysis, mechanisms of transmission of respiratory viruses, mathematical models of airborne infection transmission, and respiratory and infectious diseases epidemiology.

Personal Interests:

Professor Milton hopes to re-engage with his love of photography, to travel, and to visit with friends and family after this pandemic is under control and before the next one, for which he hopes we will be better prepared. Which is why he’s working non-stop now.

Personal Statement:
Over the last year, 2020, l felt like I was watching a train wreck that I had seen coming
for nearly 20 years. As Nell Greenfieldboyce wrote in “Shots: health news from NPR” on
December 26, 2020:

Donald Milton, a researcher at the University of Maryland, has spent a quarter-
century thinking about the transmission of respiratory viruses through the air and
has published studies showing that better ventilation in offices and dormitories is
associated with a lower risk of virus transmission.

Ten years ago, I was asked to comment on the HHS Pandemic Influenza Plan and at
that time I noted that the national plan to shut down schools and businesses would be a
disaster bringing our economy to a halt – we needed to acknowledge the role of
aerosols in spread of pandemic influenza and prepare by making our schools and
workplaces safe. You know how this story played out.

Greenfieldboyce went on to write:
He's hoping the experience of this past year will lead to better engineering
solutions being put in place to improve the overall safety of houses and other
indoor spaces — things like enhanced ventilation, air filters or special lights up by
a room's ceiling to disinfect the circulating air.

"How can we make indoor spaces safe so that we can keep our economy
running and fight a pandemic without all the damage that we are seeing from the
interventions that we have been forced to take this year?" says Milton. "I want to
see us understand how it is that you can make a restaurant a safe place to be
during a flu season and during a pandemic."

He thinks it's doable, but he worries that once vaccines get the coronavirus in
check, people will just lose interest — until the next time there's a new virus that
can be transmitted through the air.

Maybe the continuing threat of more transmissible and possibly more lethal variants will
keep our attention long enough to do the research and to address the problems. I will
keep trying to do the work and hope that we do better next time.

Education and Training
  • Dr.P.H., Environmental Health, Harvard University;
  • M.O.H., Harvard University,
  • M.D., Johns Hopkins University;
  • B.S., Chemistry (Cum Laude), University of Maryland Baltimore County
  • Residency in Internal Medicine: Emory University - Grady Hospital, Atlanta, GA and Boston University Hosptal
  • Residency in Occuapational and Environmental Medicine, Harvard School of Public Health
  • Board Certified in Internal Medicine and Occupational and Environmental Medicine
Honors and Awards
  • 1983 Lloyd Hyde Research Award, Emory University School of Medicine
  • 2002 Best Paper Award 1999-2000, International Society for Indoor Air Quality and Climate, Indoor Air Journal
  • 2005 Best Paper Award 2002-2003, International Society for Indoor Air Quality, Indoor Air Journal
  • 2008 Elected Fellow, International Society for Indoor Air Quality
  • 2009 Harriet Hardy Award , New England College of Occupational & Environmental Medicine

View all of Dr. Milton's publications on Google Scholar.

1. de Assis RR, Jain A, Nakajima R, Jasinskas A, Felgner J, Obiero JM, Norris PJ, Stone M, Simmons G, Bagri A, Irsch J, Schreiber M, Buser A, Holbro A, Battegay M, Hosimer P, Noesen C, Adenaiye O, Tai S, Hong F, Milton DK, Davies DH, Contestable P, Corash LM, Busch MP, Felgner PL, Khan S. Analysis of SARS-CoV-2 antibodies in COVID-19 convalescent blood using a coronavirus antigen microarray. Nat Commun. 2021 Jan 4;12(1):6. PMCID: PMC7782488

2. Bueno de Mesquita PJ, Nguyen-Van-Tam J, Killingley B, Enstone J, Lambkin-Williams R, Gilbert AS, Mann A, Forni J, Yan J, Pantelic J, Grantham ML, Milton DK. Influenza A (H3) illness and viral aerosol shedding from symptomatic naturally infected and experimentally infected cases. Influenza Other Respir Viruses. 2021 Jan;15(1):154–163. PMCID: PMC7767952

3. Adenaiye O, Bueno de Mesquita PJ, Wu Q, Hong F, Lai J, Chen S, Milton DK, Prometheus@UMD Consortium. The effect of COVID-19 stay-at-home order and campus closure on the prevalence of acute respiratory infection symptoms in college campus cohorts. Influenza Other Respir Viruses. 2021 Mar 4; PMID: 33665959

4. Zhu S, Jenkins S, Addo K, Heidarinejad M, Romo SA, Layne A, Ehizibolo J, Dalgo D, Mattise NW, Hong F, Adenaiye OO, Bueno de Mesquita JP, Albert BJ, Washington-Lewis R, German J, Tai S, Youssefi S, Milton DK, Srebric J. Ventilation and laboratory confirmed acute respiratory infection (ARI) rates in college residence halls in College Park, Maryland. Environ Int. 2020 Apr;137:105537. PMCID: PMC7112667

5. Prather KA, Marr LC, Schooley RT, McDiarmid MA, Wilson ME, Milton DK. Airborne transmission of SARS-CoV-2. Science. 2020 Oct 16;370(6514):303–304. PMID: 33020250

6. Nguyen-Van-Tam JS, Killingley B, Enstone J, Hewitt M, Pantelic J, Grantham ML, Bueno de Mesquita PJ, Lambkin-Williams R, Gilbert A, Mann A, Forni J, Noakes CJ, Levine MZ, Berman L, Lindstrom S, Cauchemez S, Bischoff W, Tellier R, Milton DK, EMIT Consortium. Minimal transmission in an influenza A (H3N2) human challenge-transmission model within a controlled exposure environment. PLoS Pathog. 2020;16(7):e1008704. PMCID: PMC7390452

7. Morawska L, Tang JW, Bahnfleth W, Bluyssen PM, Boerstra A, Buonanno G, Cao J, Dancer S, Floto A, Franchimon F, Haworth C, Hogeling J, Isaxon C, Jimenez JL, Kurnitski J, Li Y, Loomans M, Marks G, Marr LC, Mazzarella L, Melikov AK, Miller S, Milton DK, Nazaroff W, Nielsen PV, Noakes C, Peccia J, Querol X, Sekhar C, Seppänen O, Tanabe S-I, Tellier R, Tham KW, Wargocki P, Wierzbicka A, Yao M. How can airborne transmission of COVID-19 indoors be minimised? Environ Int. 2020 May 27;142:105832. PMCID: PMC7250761

8. Morawska L, Milton DK. It Is Time to Address Airborne Transmission of Coronavirus Disease 2019 (COVID-19). Clin Infect Dis. 2020 Jul 6;71(9):2311–2313. PMCID: PMC7454469

9. Milton DK. A Rosetta Stone for Understanding Infectious Drops and Aerosols. J Pediatric Infect Dis Soc. 2020 Jul 24;9(4):413–415. PMCID: PMC7495905

10. Leung NHL, Chu DKW, Shiu EYC, Chan K-H, McDevitt JJ, Hau BJP, Yen H-L, Li Y, Ip DKM, Peiris JSM, Seto W-H, Leung GM, Milton DK, Cowling BJ.  Respiratory virus shedding in exhaled breath and efficacy of face masks. Nat Med. 2020;26(5):676–680. PMID: 32371934

11. Fennelly KP, Acuna-Villaorduna C, Jones-Lopez E, Lindsley WG, Milton DK. Microbial Aerosols: New Diagnostic Specimens for Pulmonary Infections. Chest. 2020 Mar;157(3):540–546. PMCID: PMC7062556

12. Chia PY, Coleman KK, Tan YK, Ong SWX, Gum M, Lau SK, Lim XF, Lim AS, Sutjipto S, Lee PH, Son TT, Young BE, Milton DK, Gray GC, Schuster S, Barkham T, De PP, Vasoo S, Chan M, Ang BSP, Tan BH, Leo Y-S, Ng O-T, Wong MSY, Marimuthu K, Singapore 2019 Novel Coronavirus Outbreak Research Team. Detection of air and surface contamination by SARS-CoV-2 in hospital rooms of infected patients. Nat Commun. 2020 May 29;11(1):2800. PMCID: PMC7260225

13. Bueno de Mesquita PJ, Noakes CJ, Milton DK. Quantitative aerobiologic analysis of an influenza human challenge-transmission trial. Indoor Air. 2020 Nov;30(6):1189–1198. PMCID: PMC7687273

14. Milton DK, Youssefi S, Hering SV, Lewis, Gregory S. Aerosol Collection System and Method [Internet]. US 10,502,655 B2, 2019 [cited 2019 Apr 27]. Available from:;+Milton&oq=Youssefi;+Milton

15. Yan J, Grantham M, Pantelic J, Bueno de Mesquita PJ, Albert B, Liu F, Ehrman S, Milton DK, EMIT Consortium. Infectious virus in exhaled breath of symptomatic seasonal influenza cases from a college community. Proc Natl Acad Sci USA. 2018 Jan 30;115(5):1081–1086. PMCID: PMC5798362

16. Milton DK, Fabian MP, Cowling BJ, Grantham ML, McDevitt JJ. Influenza virus aerosols in human exhaled breath: particle size, culturability, and effect of surgical masks. PLoS Pathog. 2013 Mar;9(3):e1003205. PMCID: PMC3591312

17. Roy CJ, Milton DK. Airborne transmission of communicable infection--the elusive pathway. N Engl J Med. 2004 Apr 22;350(17):1710–1712. PMID: 15102996

18. Rudnick SN, Milton DK. Risk of indoor airborne infection transmission estimated from carbon dioxide concentration. Indoor Air. 2003 Sep;13(3):237–245. PMID: 12950586