The covid-19 virus pandemic has created substantial concern for our customers in touching a hold or piece of equipment someone else has previously touched. Although the CDC no longer considers “touch” a means of transmission, it may remain a concern for the public. For indoor climbing gyms this can be a considerable detriment as climbs and holds are used by successive climbers. But what if those fears could be allayed?

Following is a summary of a literature search concerning salts and survival of viruses. This research has been ongoing for years and has bearing on climbing because our climbers chalk, magnesium carbonate and calcium carbonate are defined chemically as salts.

  1. Research published in the journal Nature evaluated surgical mask filter effectiveness as a virus deactivation system when the filter was soaked in a salt solution. The article describes how virus is destroyed through evaporation and salt-recrystallization when an aerosolized virus-containing droplet of water lands on salt (in this case table salt, sodium chloride). Virus was destroyed in less than 5 minutes. It is important to note 3 different H1N1 viruses were tested.
  2. Research published in the Journal of Virology describes the limited pH range in which viruses are pathogenic.

How do these studies pertain to indoor climbing gyms and their operational safety?

  1. In the first article, the authors suggest the same mechanism described with sodium chloride (table salt) can be expected from any salt with a critical relative humidity (RH%) greater than 75% — the RH% of the salt used in their experiment.
    1. Note: critical relative humidity (RH%) is the humidity at which the salt begins to absorb water from the atmosphere
  2. The critical RH% of both magnesium carbonate and calcium carbonate, the primary components of climbers chalk, exceeds 95%.
  3. In the second article, the authors describe the pH activity range for viruses indicating virus, although present, is not pathogenic above a given pH
    1. Note: pH is a measure of acidity or alkalinity: lower number is acid. Tap water is generally neutral at around 7.
  4. Thus, I believe it consistent and logical to suggest climbers chalk will deactivate viruses in the same manner described in these articles.
  5. Further, I believe it consistent with the research, the same mechanism will occur with sweaty palms and fingers since climbers continually apply chalk to their hands and our holds are covered in chalk.
    1. Physicians suggested chalk may provide additional benefits: once a climbers hands are covered with chalk, climbers are less likely to touch their mouth, nose, or eyes; chalk acts a barrier, possibly better than gloves, and this “barrier” is continually renewed as climbers “re-chalk”; chalk is present on nearly all surfaces within our gyms, thus, the entire gym may be hostile to virus.

At Gemstone Climbing Center, we tested our boulder pad, walls and volumes, holds, and rope flooring for presence of chalk (we used pH test strips and tap water to test. A high pH indicated presence of chalk).

As expected, chalk was present on all surfaces especially horizontal surfaces and through-out the gym, fitness area, behind walls, superstructure, counter tops, etc. Not so much in locker rooms and yoga studio, but it was still there. Our HVAC system is a combination of electrostatic precipitators and high-end paper filters and they get coated with chalk (we use high pressure air to clean filters).

Although we cannot definitively prove the covid-19 virus is destroyed in our gyms, I believe the research strongly suggests the chalk used by climbers can inactivate and destroy virus.

I believe the research has valid application to our gyms and we are now making progress to answer the BIG QUESTION: “can aerosolized droplets of virus survive on climbers chalk?”

If viruses cannot survive on climbers chalk, we win and our customers win. But also, gymnastics gyms, ninja warrior/spartan/cross fit/obstacle course gyms, fitness gyms and all their customers win. And not just in the “short term” as virus associated illnesses occur every year.

UPDATE: I had been unable to interest an institution in the U.S. to conduct the research to answer the question. However, just as climbers are not deterred by falling off a hard route, John Bergman and Scott Rennak of the Climbing Business Journal published these ideas on Chalk/Virus. Jeremy Wilson of the Association of British Climbing Walls, picked it up and began talking with other climbers. On May 21, I received notification De Montfort University, England, had agreed to do the research. It is now “in queue.” We are hoping for results in 4-6 weeks.


Don Campbell

Gemstone Climbing


References and summaries:

  1. Nature, ( Scientific Reports 7, article no. 39956, 2017. Quan, Rubino, Lee, Koch, and Choi, University of Alberta). “Universal and reusable virus deactivation system for respiratory protection.”

The link to this article is

In the Discussion and Conclusion section are the following: (my explanations in italics):

“Rapid loss of HA activity and viral infectivity on salt-coated filters can be explained by physical destruction of virus during recrystallization of coated salts.  When the salt-coated filter is exposed to virus aerosols, salt crystals below the aerosol droplet dissolve to increase osmotic pressure to virus. Due to evaporation, the salt concentration of the droplet significantly increases and reaches the solubility limit, leading to recrystallization of salt. As a consequence, virus particles are exposed to increasing osmotic pressure during the drying process and are physically damaged by crystallization.”

“From microscopic analysis, aerosol drying time was about 3 min, indicating that destruction of virus observed at 5 min is associated with drying-induced salt crystallization. Physical damage of virus due to crystallization was similarly reported as a major destabilizing factor of inactivated influenza virus.” (see figure a,b)

“Notably, (in this study) for demonstration of the concept of salt-recrystallization based virus deactivation system, NaCl salt was used, which has a critical RH of 75% at 30 °C. However, salts with higher critical RH can be easily used, such as ammonium sulfate, potassium chloride and potassium sulfate, which have critical RH of 80%, 84% and 96.3% at 30 °C, respectively. This suggests that salt-coated filters may be developed for specific environmental conditions.”

The critical RH is the relative humidity at which the salt will absorb water. Mg and Ca carbonates have an RH above 95% similar to potassium sulfate.

“In fact, the destruction mechanism of viruses solely depends on the simple, yet robust naturally occurring salt recrystallization process, combining the destabilizing effects of salt crystal growth and concentration increase during drying of aerosols.”

“Therefore, we believe that (a) salt-recrystallization based virus deactivation system can contribute to global health by providing a more reliable means of preventing transmission and infection of pandemic or epidemic diseases and bioterrorism.”

Figure a,b) HA activity (a) and virus titer (b) displaying the effects of incubation time on the remaining activity of virus (n = 4–8, mean ± SD).

The article has electron micrographs of the virus at the various times during incubation. As the experiments were done with mice, it is important to know there was 100% survival of those mice where aerosolized virus was sent through filters with the highest concentration of salt.


  1. the Journal of Virology (93 e00058-19, June 2019. Singanayagam United Kingdom). “Influenza Virus with Increased pH of Hemagglutinin Activation (HA) has Improved Replication in Cell Culture but at the Cost of Infectivity in Human Airway Epithelium.”


This article discusses pH dependency of virus pathogenicity. Hemagglutinin (HA) is the stalk of corona virus and fusion is the process by which a virus infiltrates into a host cell. The virus envelope (the spikes on the corona) attaches to the host cell, opens it up, then merges with the host cell. If fusion can be interrupted or stopped, as with pH, the virus is inactivated.


Schematic of the relationship between HA pH of fusion, virulence, and airborne transmissibility. In order to infect and replicate in humans (blue line) or mice (purple line), influenza viruses have an optimum pH of fusion that is lower than that in domestic poultry (green line). This becomes important when assessing for zoonotic influenza viruses with pandemic potential. For an influenza virus to become a successful human pathogen, it must be able to sustain human-to-human airborne transmission, which requires a more stable HA, as is found in human seasonal viruses. Conversely, anti-influenza therapeutics that target the fusogenic ability of the influenza HA may drive virus to evolve an increased pH of fusion, with consequences on the balance between virulence and transmissibility.