Salt therapy has been used for millennia, but the modern therapy can be traced to the salt mines and caves in Europe and Russia from the early XIX century. In the beginning of XIX century a Polish physician, Dr. Feliks Boczkowski, noticed that salt mine workers had fewer skin and respiratory health complaints as compared to other miners. He concluded that the inhalation of micro-sized salt particles in the mines, and the quality of the environment below the Earth’s surface, including optimal air pressure and circulation, and humidity and temperature may have beneficial health effects. In 1893, the first health resort at the “Wieliczka” Salt Mine in Poland was founded and opened by Dr. Boczkowski.
During World War II, the Kluter salt caves in Germany were used as a shelter during heavy bombing. In 1949, Dr. Spannahel observed that people hiding in the caves for prolonged periods had experienced relief from their respiratory problems.
In 1958, the Polish professor and physician at the "Wieliczka" Salt Mine, Mieczyslaw Skulimowski, started regular treatment of patients in the salt chambers. After 1990’s, salt therapy protocols became available to other countries and developed into commercial and wellness settings in Eastern and Western Europe, North America, and Australia.
TYPES OF SALT THERAPY
The use of salt therapy extends to many applications, such as inhalations of the air in salt caves (speleotherapy), built chambers (halotherapy), breathing air on sea shores, saline gargling, or nasal irrigation.
Speleotherapy requires the presence of fine aerosol elements (sodium, potassium, magnesium, and calcium), a stable air temperature, moderate to high humidity, as well as the absence of airborne pollutants and pollens (Horvath, 1986).
Halotherapy is performed in halochamber, a special room with salt-coated walls and floor. This environment also has a cool air temperature (18-24°C) and a stable humidity (relative air humidity 40-60%). During the therapy, a dry sodium chloride aerosol containing particles of 1-5 µm dimeter is produced in this room by a special nebulizer, the halogenerator which pushes these particles into the room (halochamber). The concentration of the salt in the air of the room is between 1-16 mg/m3. The session therapy lasts for 30-60 minutes, and it is usually repeated 10-20 times (Endre, 2015). This form of halotherapy is also called an active salt room. The second type, called a passive salt room, is a man-made environment filled with varying types of salt but without a halogenerator. Often, passive salt rooms are designed to control the climate by regulating the airflow, humidity and temperature to allow for an allergen- and pollutant-free environment. Passive salt rooms attempt to mimic the conditions present in natural salt caves, but in an artificial environment.
MECHANISMS INVOLVED IN THE DEVELOPMENT OF LUNG DISEASES
Many lung diseases result in remodelling of the lung tissue, changes in the differentiation profile of the airway epithelium, airway obstruction, mucus overproduction, reduced mucociliary clearance and increased inflammation (Kuyper et al., 2003¸ Wang et al., 2012 Boulet et al., 2015). The cellular and molecular mechanisms involved in the initiation and progression of lung diseases are still not well defined. However, environmental factors, including cigarette smoking and occupational exposure to various irritants, as well as genetic risk factors, play a fundamental role in the susceptibility to lung damage.
LUNG'S PROTECTIVE MECHANISMS
The lungs are protected by several physiologically regulated protective mechanisms. The airways are covered by a layer of fluid and mucus that is constantly being moved by cilia from the distal to proximal part of the lung airways. This mucociliary clearance is an innate defence mechanism that protects the respiratory system from harmful consequences of inhaled biological, chemical, and physical agents. The efficacy of that process depends on the volume of the epithelial lining fluid, the rheological properties of the mucus, and ciliary activity (Wanner et al., 1996; Knowles and Boucher, 2002). Damage to the mucociliary system inhibits the removal mechanism, resulting in pathogen overgrowth and bronchial inflammation. Those cause further injury and structural changes in the lungs (Lai and Rogers, 2010¸ Zhao et al., 2014).
HOW SALT THERAPY WORK?
The main effective factor in halo- and speleotherapy is the sodium chloride aerosol with a particle size of 1-5 µm, which is optimal to allow it to penetrate into all layers of the respiratory tract system. In addition to antibacterial and anti-inflammatory properties, the salt particles also facilitate mucociliary transport and reduce the IgE level (Dityatkovskayaya et al., 1993). IgE is a type of antibody which plays a role in allergic diseases, anaphylactic reaction and immune response against parasitic infections. The reduction of the IgE level is especially important in patients with asthma. Clinical trials (Chervinskaya, 1995; Gorbenko et al., 1996; Abdrakhmanov et al., 2000; Grigor'eva, 2003; Horowitz, 2010; Oprita et al., 2010; Nurov, 2010; Kendrova et al., 2016; Kostrzon et al., 2019) have confirmed that salt therapy is an effective option for relieving symptoms and improving functional parameters in:
sinusitis
bronchiectasis
chronic bronchitis
mild and moderate asthma
chronic obstructive pulmonary disease (COPD)
cystic fibrosis
as well as skin disorders such as eczema and dermatitis.
Moreover, inhaled salt protects against bronchial hyperreactivity and oedema of the bronchial mucosa, decreases inflammation and reduces the frequency of the respiratory tract infections. Speleotherapy, halotherapy and hypertonic saline therapy result in (Horvath, 1986; Chervinskaya, 1995; Maev, 1999; Farkhutdinov et al., 2000; Opria et al., 2010; Nurov, 2010; Miraglia et al., 2012; Kendrova et al., 2016; Kostrzon et al., 2019; Panta et al., 2021):
easier sputum expectoration
reduced sputum viscosity
relief of cough and shortness of breath
improved pulmonary ventilation and respiratory lung function tests
improved local immunity
increased tolerance to physical exercise
improved quality of life
decreased anxiety and depression
shorter length of hospitalization due to respiratory disease
decreased inflammatory exudates and inhibited DNA and RNA virus replication, including influenza, SARS-CoV-2 other respiratory viruses.
RARE SIDE EFFECTS AND CONTRAINDICATIONS
Salt therapy is 100-percent natural, drug-free, and generally safe. During the treatment, the patient might experience some coughing, and secretions might become more abundant, these effects are considered as being due to clearing of the respiratory tract. Irritations of the mucous membrane or skin are rarely seen. Occasionally a tickly throat or redness of the conjunctiva or slight skin rash may occur, and these may last for 3-5 days. Salt therapy should not be used in feverish infections, in acute active tuberculosis, in the 3rd stage of COPD, acute stages of respiratory disease, cardiac insufficiency, bleeding or if the patient is spitting blood, or in cases of unstable or uncontrolled hypertension, hyperthyroidism, or alcohol or drug intoxication.
CONCLUSIONS
Salt therapy is a complementary treatment suitable for numerous respiratory diseases. The therapeutic effect results from the curative properties of dry sodium chloride aerosol particles and the method of its administration. Salt therapy can be combined with other physical therapy methods, as well as with pharmaceutical products. As a method with negligible side effects, conducted in a pleasant environment, it has also a beneficial effect on the psychological health of the patients. Therefore, salt therapy should be considered in the holistic rehabilitation of patients with respiratory disorders.
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