speleotherapyHalotherapy (HT, from Greek halos=salt) uses dry aerosol microparticles of salt and, in one version, minerals to treat respiratory diseases. HT seeks to replicate the conditions of speleotherapy (from Greek speleos=cave), a treatment that has been practiced in old salt mines of Eastern Europe since the early 19th Century.

Halotherapy belongs to the category of the physical therapies–non-drug treatments of diseases, many associated with the spa treatments of Eastern Europe. In the former Soviet Union, medical researchers engaged in a concerted effort to develop physical therapies in order to avoid the costs and side effects of drug therapy as well as microbial and tumor resistance. Russia has become a world leader in developing and testing new and increasingly effective physical therapies.

Most of the dozens of clinical trials thus far, mainly reported in Russian-language journals, have focused on HT as a treatment of asthma and chronic bronchitis. But HT may also be effective as a main or adjuvant therapy across the entire range of upper and lower respiratory tract diseases and potentially against certain other diseases as well. Respiratory diseases are a major cause of morbidity and mortality worldwide. Asthma has become ever more prevalent in industrialized societies, with special impact on children. Meanwhile, cigarette smoking has spread chronic bronchitis and emphysema everywhere; in developing countries biomass cooking smoke has a similar devastating impact on women and children. The situation in especially bad in China, with its 350 million smokers and terrible air pollution. Most drug therapies of respiratory diseases have only palliative effects, and many have significant side effects. So a physical therapy like HT is much needed.

HT’s excellent action and modest cost make it a very attractive kind of medicine.

Speleotherapy

It is likely that miners and others knew about the beneficial health effects of the microclimate of salt mines for centuries before they were first described in a book published by a Polish physician in 1843. Since then, the practice of bringing patients with respiratory diseases down into salt mines for cures gradually spread throughout Eastern Europe, and it has become a standard feature of spa treatment there.

By its very nature, speleotherapy resists scientific norms. The reported healing and invigorating effects of the microclimate of salt mines are variously ascribed to the microparticles of salt floating in the air, the temperature, the relative humidity, the near or total absence of pathogens and allergens, the effects of radiation from minerals, and the tranquillity of the setting. But it is difficult to determine the relative influence of these factors, and presumably some synergy exists. In addition, each chamber in each mine has a distinct microclimate. Conducting clinical trials in such conditions is not easy. Often speleotherapy has been combined with other modalities. And many of the early clinical trial reports lacked scientific rigor. Speleotherapy also makes a great demand on patients’ time. The mines are not conveniently located for most people. The total cost is fairly significant. Determining a specific dose and tracking long-term effects of speleotherapy have proven very elusive goals.

Nonetheless, various clinical trial reports and the favorable outcomes for many individual patients have led to growing scientific attention and a devoted following for speleotherapy (for a sample report, see Horvath, 1986). They also gave the Soviet (now Russian) space agency the idea of developing microclimate optimization devices for cosmonauts that would replicate the microclimates of salt mines. Most of this work has been done in St. Petersburg.

HT Devices

In the 1980s the Russians began to build halochambers that recreated in clinics the microclimate of salt mines. These halochambers have floors and walls lined with rock salt (halite). Patients sit in the halochamber for an hour per session while music and pleasant videos are played to create a relaxed mood. Halochambers are certified as medical devices in Russia.  They are also widely used in Europe, North America, and elsewhere.

Another approach has been the desktop HT device, which has tubes for breathing in the aerosol salt or simply fills the air with microparticles of salt. Thus far no multimineral aerosol appears to have been supplied this way, though halochambers have been lined with silvinite, the rock from potash mines that contains about 60 percent sodium chloride, 35 percent potassium chloride, and 5 percent of other minerals. Pure halite is the precipitate from the shores of ancient seas, while silvinite results from the evaporation of a dead sea. Often a desktop HT device is used in combination with a halochamber.

A ceramic salt pipe from Hungary represents a third approach. The patient breathes in gently through the mouth, then exhales through the nose.

A fourth, popular device is the rock crystal lamp (Pakistan) or salt lamp (Poland), which is comprised of a largish piece of rock salt with an attached light bulb that glows through the salt and whose heat causes microparticles to become airborne.

Serious clinical studies have been done of the first two methods, where the number of microparticles per cubic meter is monitored, permitting accurate dose measurement. The ability to deliver a specified dose represents a major advantage of halotherapy over speleotherapy. Still, speleotherapy retains importance as a source of scientific evidence regarding the as-yet not well-characterized, multiple factors that deliver the therapeutic effect. Depending on the conditions of a certain salt mine or cave, speleotherapy might also prove more effective than halotherapy in a given case.

Parameters

Aerosolized microparticles larger than 10 microns in diameter are caught in the upper airways and transported up and out of the respiratory tract by the mucociliary system. In the range of 5-10 microns, they penetrate into the trachea and central bronchial area, but no farther. Only below 5 microns do the dry microparticles penetrate into every corner of the bronchi and alveoli.  Even though the salt microparticles spread over an area in the alveoli roughly the size of a tennis court, only a few milligrams of salt are needed.  So there need be no concern about the possibility of excessive salt intake from halotherapy in the case of hypertensive patients. The extremely small size, relatively low amount, and slow dosing of the microparticles also make them much less likely to provoke a hyperreactive response in asthma patients than moist hypertonic saline.

According to various authors, maintaining a room temperature in the vicinity of 18-24° C and a relative humidity below 55% can conduce to better treatment outcomes. Devices can be set to emit different amounts of salt microparticles–monitored by a microparticle counting device. The negative electrical charge on the particles, which has been measured at a high 6-10 nK/m³ (Chervinskaya, 2002), protects them against clumping and enables them to adhere to allergens and microbes in the air, forming precipitates that fall out of the air (Khan, 2016).  (Note that, in electrostatics, a large particle with a high negative charge can attract a smaller particle with a much smaller negative charge.)

Applications

Halotherapy can be used to treat many chronic respiratory and skin conditions.  It has been shown to be effective in acute respiratory infections as well.  In a randomized, single-blinded trial with placebo controls, a treatment group of 80 and a control group of 80 were treated for 12 weeks with two weekly 10-minute sessions of inhaling from a halotherapy device and an empty device, respectively.  After 3 months there were only 14 cases of acute respiratory viral infections and 104 days of symptoms in the treatment group whereas the control group had 55 infections and 585 days of symptoms (Chervinskaya, 2009).

This suggests that regular use of a home HT device or salt pipe could serve as an effective personal adjuvant therapy, in a manner parallel to gargling, in epidemics such as the COVID-19 pandemic.  HT should be tested in this role.

In theory, HT can serve as an air disinfectant like ultraviolet and various chemical disinfectants.  This would require careful matching to the unique characteristics of the space to be disinfected.  Still, for making classrooms, offices, factories, and other settings safer in normal times and especially during epidemics, this is an alluring potential application.

For further discussion of the potential applications of HT in the COVID-19 pandemic, see Halotherapy versus COVID-19.


References

Borisenko, L.V. et al. (1994), “The Use of Halotherapy in the Rehabilitation of Patients with Acute Bronchitis of a Protracted and Recurrent Course,” Vopr Kurortol Fizioter Lech Fiz Kult, Jan-Feb;(1), 11-15 [Russian]

Chervinskaya, Alina V.  Dry sodium chloride aerosol against acute respiratory infections.  Eur Respir J 2009; 34: Suppl. 53, 401s

Chervinskaya, A.V. et al. (2002), “Effects of Halogen Aerosol Therapy on Defense Characteristics of the Respiratory Tract,” Terapevticheskii Arkhiv 3, 48-52 [Russian]

Chervinskaya, Alina V. and Nora A. Zilber (1995), “Halotherapy for Treatment of Respiratory Diseases,” Journal of Aerosol Medicine 8(3), 221-232

Horvath, Tibor (1986), “Speleotherapy: A Special Kind of Climatotherapy, Its Role in Respiratory Rehabilitation,” Int Rehabil Med 8, 90-92

Khan, M.A. et al (2016), “The promising directions for the further development of halotherapy in pediatric medicine,”  Vopr Kurortol Fizioter Lech Fiz Kult, 6, 61-66 [Russian]

Krasnoshtein, A.E. et al. (1999), “Above-ground Speleoclimatic Chambers and Experience in Their Use in Bronchial Asthma,” Vopr Kurortol Fizioter Lech Fiz Kult, May-June; 3, 25-28 [Russian]

Rassulova, M.A. et al. (2000), “The Use of the Microclimate of Artificial Sylvinite Speleoclimatic Chambers in Treating Patients with Chronic Obstructive Bronchitis,” Vopr Kurortol Fizioter Lech Fiz Kult, Jan-Feb; (1), 17-21 [Russian]

Rein, M.F. and G.Z. Mandell (1973), “Bacterial Killing by Bacteriostatic Saline Solutions: Potential for Diagnostic Error,” New England Journal of Medicine 289(15), 794-795

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Kenneth J. Dillon is an historian who writes on science, medicine, and history.  See the biosketch at About Us.

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