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CLAYS AND HUMAN HEALTH

M.I. CARRETEROa, C.S.F. GOMESb AND F. TATEOc

aDepartamento de Cristalografı´a, Mineralogı´a y Quı´mica Agrı´cola, Facultad de

Quı´mica, Universidad de Sevilla, ES-41071 Sevilla, Spain

bDepartamento de Geocieˆncias, Universidade de Aveiro, P-3810-193 Aveiro, Portugal

cIstituto di Ricerca sulle Argille, CNR, I-85050 Tito Scalo (PZ), Italy

Clay minerals can be beneficial to human health by serving as active principles or

excipients in pharmaceutical preparations, in spas, and in beauty therapy medicine.

In some cases, however, these minerals can be harmful to human health. Both the

beneficial and harmful effects of clay minerals are described in this chapter.

11.5.1. BENEFICIAL EFFECTS OF CLAYS AND CLAY MINERALS

A. Historical Background

Since prehistoric times man used clay for therapeutic purposes. There are indications

that homo erectus and homo neanderthalensis used ochres mixed with water and

different types of mud to cure wounds, to soothe irritations, as a method of skin

cleaning, etc. This might be due to their mimicking animals, many of which

instinctively use minerals for such kind of purposes. The clay plates of Nippur,

Mesopotamia, which date back to about 2500 BC, contain a reference to the use of

clay for therapeutic purposes, including the treatment of wounds and the inhibition

of haemorrhages. In ancient Egypt, Pharaoh’s doctors used Nubian earth as an antiinflammatory

agent, and yellow ochre (a mixture of clay and iron oxy/hydroxides) as

a cure for skin wounds and internal maladies and as a preservative in mummification.

Likewise, Cleopatra (44–30 BC), Queen of Egypt, used muds from the Dead

Sea for cosmetic purposes (Bech, 1987; Newton, 1991; Robertson, 1996; Veniale,

1997; Reinbacher, 1999).

In the Ancient Greek period, mud materials were used as antiseptic cataplasms to

cure skin afflictions, as cicatrices, or as a cure for snakebites. Bolus Armenus, a red

clay found in the mountain caves of Cappadocia, old Armenia, present-day Turkey,

was famous as a medicinal clay, as were the so-called terras of the Greek islands

Lemnos, Chios, Samos, Isola, Milos, and Kimolos. These terras were prepared and

shaped into disks (called ‘‘earth coins’’ and used until the 19th century) that were

marked or stamped with different symbols, for example with the goat stamp, the

mark of the goddess Diana/Artemis (Bech, 1987). Among these, the terra sigillata of

Lemnos deserves particular mention, because of its astringent and absorbent properties.

The clay from Kimolos was identified as Ca2+-smectite (Robertson, 1986),

and the terra sigillata of Samos as kaolinite or illite/smectite mixed-layer mineral

(Giammatteo et al., 1997). Galeno (131–201 AD), a Greek doctor (born in Pergamo)

described medicinal muds, and used clays to deal with malaria, and stomach and

intestinal ailments.

In some civilisations, the use of clays was extended to ingesting clays for therapeutic

purposes. Aristotle (384–322 BC) made the first reference to the deliberate

eating of earth, soil, or clay by humans (for therapeutic and religious purposes).

Later, Marco Polo described how in his travels he saw Muslim pilgrims cured fevers

by ingesting ‘‘pink earth’’. This practice is still followed in certain countries and

communities for therapeutic purposes, or even to relieve famine (Mahaney et al.,

2000). The rubbing of clays into the body for therapeutic purposes was known for a

very long time. However, this custom (as practiced in contemporary spa centres) did

not become widespread in Europe until Roman times when dedicated buildings,

called ‘‘balnea’’, were erected. Later, the use of spas declined. During the 19th

century and the beginning of the 20th century spas reappeared, and were frequently

visited. Many of them continue using muds for therapeutic purposes. Some examples

are Centro Termal das Furnas in Vale das Furnas, on the island of Sa˜o Miguel

(Azores), Montecatini Terme, Ischia and Abano Terme in Italy, Karlovi Vary in the

Czech Republic, and Archena and El Raposo in Spain.

The famous Papyrus Ebers (dated about 1600 BC, but a copy of a papyrus from

2500 BC) describes some diseases and their treatment using mineral- and, particularly,

clay-based medicines. Other references to the curative powers of clays appear

in Pen Ts’ao Kang Mu, a famous old catalogue about Chinese medicine. In Roman

times similar references could be found in Dioscorides’ De Materia Medica (60 BC).

This book also has a section dealing with minerals and chemical substances used in

pharmacy. In his Natural History, Pliny the Elder (23–79 AD) also described the use

of clays, especially those found around Naples (volcanic muds), for curing stomach

and intestinal ailments. In the 11th and 12th centuries Avicena (980–1037 AD) and

Averroes (1126–1198 AD) classified and encouraged the use of medicinal muds

(Bech, 1987; Veniale, 1999a). Later, Lapidarios, dealing partially with the use of

minerals from a therapeutic perspective, would appear. Among these works is the

famous Lapidarios of the Spanish King, Alfonso X the Wise (1221–1284 AD). The

first extant Lapidario is a translation into Spanish by Yhuda Mosca and Garci Pe´rez

of Abolays’ book in Arabic that Abolays himself had previously translated from

Chaldean, although its original source is not known (Brey Marin˜ o, 1982). During the

Renaissance Pharmacopoeia appeared. These were texts that, among other drugs,

classify different minerals for medicinal uses. In addition, they described regulations

concerning their uses, such as the official codes that must be followed to produce

medicines. Their appearance coincided with the first mineralogical classifications. In

the 17th century the first scientific academies were founded, one aspect of whose

work was to document the advances of mineralogy in medico-pharmaceutical matters,

thus producing various entries in the pharmacopoeias. In the early 20th century

the development of chemistry enabled numerous minerals to be obtained through

synthesis. The use of synthetic minerals had a negative effect on the use of naturally

occurring minerals for therapeutic uses and as excipients. However, given the difficulty

and cost involved in synthesising minerals on an industrial scale, natural clay

minerals are mainly used for such purposes at present. An exception is ‘‘Laponite S’’,

a synthetic hectorite made by the Laporte Company (NL), and used as a jellifying

material in cosmetic formulations (Gala´n et al., 1985; Bech, 1987; Carretero, 2002).

B. Clay Minerals in Pharmaceutical Formulations

The use of clay minerals in pharmaceutical formulations was described by many

authors (Del Pozo 1978, 1979; Gala´n et al., 1985; Bech, 1987; Cornejo, 1990; Ga´ miz

et al., 1992; Bolger, 1995; Veniale, 1992, 1997; Viseras and Lo´ pez-Galindo, 1999;

Lo´ pez-Galindo and Viseras, 2000; Carretero, 2002), and collected in different pharmacopeias

(AA.VV., 1996, 1998, 2002a,b,c,d).

Kaolinite, talc, palygorskite, and smectites are used for therapeutic purposes in

pharmaceutical formulations as active principles or excipients. The possible use of

sepiolite as active principle or excipient in pharmaceutical formulations was also

investigated (Hermosı´n et al., 1981; Cornejo et al., 1983; Forteza et al., 1988; Ueda

and Hamayoshi, 1992; Del Hoyo et al., 1993, 1998; Viseras and Lo´ pez-Galindo,

1999; Lo´ pez-Galindo and Viseras, 2000; Cerezo et al., 2001) and there are commercial

medicine that includes sepiolite in its composition (as active principle and

excipient). The fundamental properties for which clay minerals are used in pharmaceutical

formulations are high specific area and sorptive capacity, favourable

rheological characteristics, chemical inertness, low or null toxicity for the patient,

and low price.

Use as Active Principles

As gastrointestinal protectors, antacids, and antidiarrhoeaics, clay minerals can be

administered to the patient orally in the form of pills, powders, suspensions, and

emulsions. Clay minerals are also applied topically (to the body’s exterior, or on a

limited portion of the body) as dermatological protectors or for cosmetic reasons.

Kaolinite and palygorskite are used as gastrointestinal protectors. Their therapeutic

action is based on their high specific area and sorption capacity. They adhere

to the gastric and intestinal mucous membrane and protect them, and can absorb

toxins, bacteria, and even viruses. However, since they also eliminate enzymes and

other necessary nutritive elements, their prolonged use is inadvisable. Although

smectites also have a large surface area and sorption capacity, they are not generally

used as gastrointestinal protectors. This is because smectites tend to decompose

11.5.1. Beneficial Effects of Clays and Clay Minerals 719

when they come into contact with the stomach’s hydrochloric acid (pH 2), and

probably also when they get to the bowel (pH 6).

Smectites and palygorskite are used as antacid due to thin H+ neuturalising

capacity. They are indicated in the treatment of gastric and duodenal ulcers.

Kaolinite, smectites and palygorskite are also used as antidiarrhoeaics due to their

high water adsorption capacity. By eliminating the excess water from faeces, the

material becomes more compact. Calcium smectites are also used as antidiarrhoeaics

due to the astringent action of the Ca2+ ion, which forms non-soluble, hydrated

phosphates.

Kaolinite, talc, and smectites are used as dermatological protectors. These clay

minerals can adhere to skin, forming a film that mechanically protects the skin

against external physical or chemical agents. By absorbing the skin’s secretions, and

creating a large surface for their evaporation, they also have a refreshing action.

Surface evaporation also promotes a gentle antiseptic action as it produces a waterpoor

medium that is unfavourable for the development of bacteria. This latter action

is reinforced by the capacity of these minerals to sorb dissolved and suspended

substances, such as greases, toxins, and even bacteria and viruses.

The use of these clay minerals as dermatological protectors should be preceded by

a mineralogical study of the corresponding raw materials. This is because in many

cases they contain mineral impurities such as quartz (in smectites), and chrysotile or

tremolite (in talc) that are dangerous for inhalation. For example, Bowes et al. (1977)

reported that of the 27 consumer talcum powders, purchased in the USA, 11 contained

tremolite and/or anthophyllite in proportions ranging from 0.5 to over 14%.

The use of palygorskite as a dermatological protector is not advisable. Nor does

palygorskite appear in any pharmaceutical formulation as powder because of current

doubts about its possible carcinogenic effect if inhaled (see below).

Kaolinite, smectite, talc, and palygorskite (the last one recommended only in

liquid preparations such as creams, emulsions, etc.) are used as active principles in

cosmetics. They feature in face masks because of their high capacity for adsorbing

greases, toxins, etc. They are also used in creams, powders, and emulsions as antiperspirants,

to give the skin opacity, remove shine, and cover blemishes. The 2002

market saw the appearance of a moisturising cream that contained very small particles

of mica (possibly muscovite), producing a luminous, light reflective effect.

Use as Excipients

Kaolinite, talc, palygorskite, and smectites are used as excipients in cosmetics and

pharmaceutical preparations. In the latter application, these minerals function as:

(i) lubricants to ease the manufacture of pills (talc);

(ii) agents to aid disintegration through their ability to swell in the presence of water

(smectites), or through the dispersion of fibres (palygorskite), promoting release

of the drug when it arrives in the stomach; and

(iii) emulsifying, polar gels and thickening agents because of their colloidal characteristics

(palygorskite, smectites, kaolinite) by avoiding segregation of the

 

pharmaceutical formulation’s components and the formation of a sediment that

is difficult to re-distribute.

Although all the excipients are considered to be inert, research carried out during

the last 30 years showed that interaction may occur between the drug and the clay

mineral used (White and Hem, 1983; Sa´ nchez Martı´n et al., 1988; Cornejo, 1990).

This process can influence two highly important aspects in the drug’s bioavailability:

its liberation and stability. With respect to the drug’s liberation, the interaction

between the drug and its excipient can retard the drug’s release and therefore its

absorption, lowering its levels in the blood. This phenomenon, detectable by in vitro

studies, may produce undesirable effects on a patient’s health if, for the drug to be

effective, immediate therapeutic levels in the blood are required, as in the case of

antihistamines (White and Hem, 1983). However, the slow, controlled desorption of

the drug can have a positive effect on its therapeutic action, as in the case of amphetamines

and antibiotics (Mc Ginity and Lach, 1977; Porubcan et al., 1978), or

water-resistant sun screens (Vicente et al., 1989; Del Hoyo et al., 1998, 2001). Regarding

the drug’s stability, interaction between drug and mineral excipient can

accelerate degradation of the drug with consequent loss of therapeutic activity and

increased health risk (Porubcan et al., 1979; Hermosı´n et al., 1981; Cornejo et al.,

1983; Forteza et al., 1988, 1989).

The interaction of drugs with clay mineral excipients used in pharmaceutical

preparations should be studied on a drug-by-drug basis. Doctors must also keep this

point in mind when they prescribe medication to patients. Given the high surface

reactivity of clay minerals, this interaction can occur either in the pharmaceutical

formulation itself or in the gastrointestinal tract, even though the drugs are administered

in different pharmaceutical formulations. This interaction can be detrimental

to human health and, in some cases, to human life. For example, montmorillonite

can catalyse the acid hydrolysis of digoxin, a cardiovascular tonic (Porubcan et al.,

1979). When digoxin is administered in liquid preparation (without clay minerals), it

can come in contact with montmorillonite from another pharmaceutical preparation

administered at the same time. The interaction between digoxin and montmorillonite

in the stomach (pH 2) could cause degradation of the drug. As a result, the drug loses

its therapeutic activity and the patient’s life is endangered.

C. Clay Minerals in Spa and Beauty Therapy

Kaolinite and smectites are used in spa and beauty therapy, as are illite, interstratified

illite/smectite and chlorite, and, on occasion, sepiolite and palygorskite.

Common (polymineralic) clays are also used. Besides phyllosilicates, these minerals

contain Fe-Mn-(hydr)oxides and other associated phases such as calcite,

quartz, and feldspars. The presence of these phases should be controlled, because the

final product applied to the patient should have only the required and appropriate

mineral properties for their use.

11.5.1. Beneficial Effects of Clays and Clay Minerals 721

The main properties of clay minerals determining their usefulness in spa and

aesthetic medicine, are:

(i) softness and small particle size since the application of the mud, particularly as

face mask, can otherwise be unpleasant;

(ii) appropriate rheological properties for the formation of a viscous and consistent

paste, and good plastic properties for easy application, and adherence to the

skin during treatment;

(iii) similarity in pH to that of the skin so as to avoid irritation or other dermatological

problems;

(iv) high sorption capacity. Clays can eliminate excess grease and toxins from skin,

and hence are very effective against dermatological diseases such as boils, acne,

ulcers, abscess, and seborrhoea. An organic active principle can also be incorporated

into the clay mineral before its application to the patient’s skin for

therapeutic purposes;

(v) high CEC, enabling an exchange of nutrients (K+ or Na+) to take place while

the clay mineral is in contact with the skin; and

(vi) high heat-retention capacity. As heat is also a therapeutic agent, clay minerals

are applied hot to treat chronic rheumatic inflammations, sport traumatisms,

and dermatological problems.

Smectites (bentonite clays) fulfil many of the requirements for usage in spa and

beauty therapy.

Types of Application and Therapeutic Activity

The different types of application and therapeutic activity of clay minerals in spas

and beauty therapy received much attention over the past 20 years (Messina and

Grossi, 1983; Torrescani, 1990; Barbieri, 1996; De Bernardi and Pedrinazzi, 1996;

Novelli, 1996; Martı´n Dı´az, 1998; Benazzo and Todesca, 1999; Lotti and Ghersetich,

1999; Nappi, 2001; Carretero, 2002).

Clays can be used mixed with water (geotherapy), mixed with sea or salt lake water

or minero-medicinal water, and then matured (pelotherapy), or mixed with paraffin

(paramuds). These three methods are used in spas and in beauty therapy. In geotherapy

and pelotherapy the application form can be as face masks, cataplasms, or

mud baths, depending on the body area to be treated, although in some spas they are

also used for corporal massages. Application temperature (hot or cold) depends on

the therapeutic aims. The paramuds are applied only as cataplasms, and always hot.

Face masks are used mainly in beauty therapy. Cataplasms are used in spas and in

beauty therapy, when the mud is applied to only a small area of the body.Mud baths

are preferentially used in spas, as the area under treatment is extensive. Application

is carried out by submerging part of the body (bathing the arms, hands, or feet) or

the whole body in a bowl or bath filled with a mixture of clay and water. The

application of face masks and cataplasms is carried out in layers of between 1 and

5 cm for 20–30 min. When applied hot (40–45 1C) cataplasms are covered with an

impermeable material to conserve the heat. In most cases the paste is recycled from

one patient to another.

Hot application is recommended in geotherapy, pelotherapy or paramuds in

beauty therapy for the following therapeutic purposes:

(i) to moisturise the skin, since during application the perspiration produced cannot

evaporate as the paste is covered with an impermeable material. This perspiration

soaks into the upper layers of the epidermis, moisturising it from

within. Moreover, after application, the skin is in a hyper-porous state, which

means cosmetic substances will be easily absorbed by the corneous layer, reaching

the deepest layers of the epidermis;

(ii) to treat compact lipodystrophies in their initial evolution when they need preventive

care but cannot be treated more aggressively, and before the application

of cosmetics;

(iii) to retard the development of cellulite, given that they stimulate venous and

lymphatic circulation in the application area and that they act as antiinflammatories;

and

(iv) for cutaneous cleaning and treating dermatological conditions such as blackheads,

spots, acne, ulcers, abscess, and seborrhoea. Heat promotes perspiration

and the flow of sebaceous secretions in a fluid state, and their sorption by the

clay mineral. Heat also opens the pylosebaceous orifices, improving sorption of

the cosmetic substances.

Hot clay application produces a sensation of heat in the area treated, as well

as vasodilatation, perspiration, and the stimulation of cardiac and respiratory frequency.

As this creates a stimulatory, antiphlogistic, and analgesic action, such

applications are recommended in spas, for the two following diseases: (i) chronic

rheumatic processes including degenerative osteoarthrosis in any part of the body,

dysendocrine arthropathies, spondilo-arthritis ankylopoietic, spondylosis, myalgias,

neuralgias and (ii) sequelae of osteo-articular injuries, fractures, dislocations; disorders

following vasculopathies.

We should note that hot application is contra-indicated in areas of the body with

circulatory problems (e.g., varicose veins), and in the acute and sub-acute phases

of rheumatic processes, discompensated cardiopathies, tuberculosis, and renal or

hepatic deficiencies. In acute pathologies (inflamed or congested areas), the application

temperature must be lower than body temperature (cold muds). Here the

application produces a cooling of the area under treatment, and since the mixture

is a good conductor of the heat given off by the inflammation, it acts as an

anti-inflammatory agent. The mixtures can also be used cold in liquid-retention

problems.

Pelotherapy

Of the three types of application of clay minerals in spas and beauty therapy,

pelotherapy is the most favoured, because the maturation process improves the

therapeutic properties of the final product (peloid) applied to the patient.

11.5.1. Beneficial Effects of Clays and Clay Minerals 723

The International Society of Medical Hydrology defines ‘‘peloid’’ as ‘‘ya natural

product consisting of a mixture of sea, salt lake, or minero-medicinal water (liquid

phase), with organic and inorganic material (solid phase) produced by biological

action (humus) and geological action (clay minerals)’’.

A comprehensive report on peloid preparation, particularly on the maturation

process, is not available. However, much progress was made in this direction by the

Gruppo Italiano of AIPEA who sponsored two meetings (Veniale, 1996, 1999b) and

published a catalogue of Italian ‘‘clay geomaterials for peloids’’ (Veniale, 1999c). Since

Italy has an exceptional tradition of thermal treatments, the catalogue and meetings

provide a snapshot of pelotherapy, with about 30 spas collaborating to varied extents

on compiling the catalogue. In recent years there were other important contributions

to the knowledge of pelotherapy (Ferrand and Yvon, 1991; Veniale and Setti,

1996; Yvon and Ferrand, 1996; Veniale, 1997; Summa and Tateo, 1998; Bettero et al.,

1999; Cara et al., 1999; Gorgoni et al., 1999; Jobstraibizer, 1999; Minguzzi et al., 1999;

Summa and Tateo, 1999; Veniale et al., 1999; Cara et al., 2000a, 2000b; Sa´nchez et al.,

2000a, 2000b; Gomes and Silva, 2001; Carretero, 2002; Sa´ nchez et al., 2002).

Peloid preparation varies from place to place. Depending on the particular spa

tradition, the maturation process ranges from a few months to two years. Some spas

use naturally matured clays collected from a spring basin, others collect the peloid

from saline pools. The majority of spas, however, use artificial ponds where the

natural (‘‘virgin’’) clay is mixed with mineral, thermo-mineral, or sea water that

issues in the vicinity of the spas or inside the spa buildings. The clay is placed in the

ponds for some months, during which period it is periodically shaken. The water

may be stagnant, periodically renewed, or, more rarely, continuously flowing

through the ponds. Interestingly, many spas initially used local clays but when these

ran low, switched to commercial clays, or a mixture of local and commercial

materials. An alternative strategy, adopted by some spas, is to recycle the material

(after use on a patient), that is, the ‘‘exhausted’’ peloid is again matured. It is

assumed that all harmful and hazardous elements, taken up from the previous

patient, are removed during re-maturation.

Maturation is a very complex process involving water and a multiplicity of

materials, including minerals (the mud is usually not mono-mineralic), inorganic

solutes, biogenic components, and organic molecules as well as different physicochemical

conditions, such as temperature, Eh, and pH. Furthermore, many of these

parameters are modified during the maturation period (cycling of temperature, light,

hydrologic regime, shaking time). This can influence the manner in which certain

materials develop. The length of maturation is a key parameter. The three main

factors controlling peloid properties are raw clay composition, water composition,

and mixing mode (‘‘maturation’’). During maturation organic substances as well as

macro- and micronutrient elements present in the water are taken up by the peloid

and can be released during application to the human body.

The maturation process improves some physical properties of the clay minerals,

such as heat retention capacity, rheology, and adhesion. At the same time, some

changes in mineralogy and organic matter take place. These modifications improve

the therapeutic effect of clay in pelotherapy.

With regard to specific heat, Ferrand and Yvon (1991) published a report on

mixtures of clays. The thermal behaviour of several mixtures of kaolinite, bentonite,

silt, and sand was tested and the temperature was measured at an appropriate and

constant viscosity. The authors propose a lineal equation for the calculation of the

specific heat, in function of the current in water. Likewise, Cara et al. (2000a) propose

a similar formula to that of Ferrand and Yvon (1991) to calculate the specific

heat of (Sardinian) bentonites. In agreement with the previous work, the specific heat

was dependent on the smectite content of the bentonite. Although this investigation

was not yet carried out with peloids (only with mixed water-clay, without maturation),

the findings are important. By extrapolating the results to pelotherapy, heat

dissipation during peloid treatment could be predicted.