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Alcohol (a.k.a. ethyl alcohol) has long been
used by the pharmaceutical industry as a solvent, penetration-enhancer,
disinfectant and preservative. Many so-called ‘natural’
skin-care products, e.g. the Dr Hauschka range, resisting
modern preservative innovations, still persist in this questionable
practice, often proudly claiming to be “free of artificial/synthetic/chemical
preservatives” or even “preservative free”. Whilst
ethyl alcohol exists widely in nature, it does not participate constructively
in the cells of living higher organisms. It is, in fact, a waste product
consequential to fermentation by lower organisms during the decomposition
of dead and/or dying organic matter.
Alcohol, used as a herbal extractive solvent
(tincture) or a preservative in skin-care products is not strictly
natural. It is artificial, indeed synthetic, even if the raw materials
are potatoes or grains and sugars and yeasts, since it is not harvested
from within nature, but rather is synthesised via a man-made industrial
laboratory process that is optimised under controlled conditions
that do not spontaneously exist in nature. At best, it may be nature-identical.
Dr Hauschka hypocritically malign the safer nature-identical
parabens, yet acknowledge having 7-12% alcohol in their
skin-care products, a concentration simply never occurring
in nature and significantly toxic to skin cells.
Alcohol is bacteriostatic and fungistatic
at 10% and reliably bactericidal and fungicidal at 30 and 35% respectively
(Victor Lorian [Editor], Antibiotics
in Laboratory Medicine, Lippincott Williams & Wilkins, Philadelphia,
USA, 2005). Even at such high concentrations, alcohol
lacks the residual antimicrobial activity that is prerequisite to
ensuring consumer protection from microbial decomposition of their
higher ‘organic’ content and toxic byproducts thereof.
Due to its high volatility and eventual metabolism in the skin (to
more toxic compounds), once alcohol-preserved products are applied
to the body, efficacy against microbes is relatively short-lived,
yet dermal cytotoxicity persists. Such products dry the skin and
must be formulated with inappropriately heavy occlusive emollients
such as castor oil and/or lanolin (more suited to ointments) to
retard evaporation and mask the presence of dying and dead skin.
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While the antibacterial efficacy
of alcohol as a topical antimicrobial has been well documented, its
effects on living tissue and the process of wound healing remains
controversial. Because of the cytotoxicity of alcohol, researchers
have suggested that one should use it topically at a dilution of up
to 1:1,000 of commonly used concentration and for a short period only
(Pyo H et al, Korean J Dermatol, 33(5),
1995). Alcohol used as an antiseptic or preservative can
effectively kill bacterial and fungal cells, but will just as effectively
kill healthy cells (Biology 1030, Dept
of Biological Sciences, Wayne State University, 1998).
Clearly therefore, daily applications of alcohol to the skin
at more than 50-100 times the cytotoxic concentration, as with the
Dr Hauschka skin care products (and perhaps similarly many others)
in this modern age, is a highly questionable practice.
Let us evaluate the skin cytotoxic potential of alcohol
(whatever its source, but restricted to ethyl alcohol - hereafter
referred to as alcohol, as used by e.g. Dr Hauschka
and other so-called natural / organic manufacturers). When alcohol
was tested for toxicity in dose response measurements on histocultured
skin exposed to various concentrations of alcohol for five minutes
and the cell types (epidermal, dermal, and follicle cells) within
the intact skin were observed for toxicity, it was determined that
before alcohol exposure, most of the cells were viable, but subsequent
exposure to alcohol caused more epidermal and dermal cells to be
nonviable with increasing concentration of alcohol, which killed
cells independent of type (Li L
et al, Proc Natl Acad Sci USA, 88:1908, 1991).
Alcohol is a significant penetration-enhancer through an
otherwise normal skin barrier, primarily due to the extraction
of intercellular lipids from the stratum corneum. Compromised
skin barrier function increases susceptibility for damage of the
skin and permeability by other chemicals. (Smith
E and Maibach H, Percutaneous Penetration Enhancers, CRC Press,
1995); (de Haan P et al, In: Pieter van der Valk & Howard Maibach
(Eds.), The Irritant Contact Dermatitis Syndrome, Informa Health
Care, 1996) Substances applied to the skin can diffuse
across the protein/lipid barrier into keratinocytes below. Facial
skin is even more permeable, which is of consequence because many
alcohol-containing cosmetics, creams, lotions and gels are commonly
regularly applied to the face. (Neuman
M et al, Alcohol, 26(3), 2002) Ethanol can be a skin
allergen in immediate and delayed hypersensitivity by external or
internal exposure and can produce subjective irritation, irritant
contact dermatitis and non-immunologic contact urticaria (Ophaswongse
S, Maibach H, Contact Dermatitis, 30:1, 1994)
In recent experiments, erstwhile collaborators of mine (Dept Clinical
Pharmacology, Dermatology & Medicine, Sunnybrook and Women’s
Health Sciences Centre, Canada) exposed human skin cells to 40 mM
of alcohol (average blood alcohol concentration of an adult after
3 glasses of wine - much less than the quantity deliberately formulated
into many cosmetics, in particular so-called ‘organic’
products and hence an increasingly common occurrence). Alcohol-exposed
cells released pro-inflammatory cytokine tumour necrosis factor-alpha,
which initiated disruption of mitochondrial membrane potential and
cell death. Electron microscopy revealed that alcohol exposed human
skin cells, even at very low concentrations caused organelle damage,
condensed chromatin, decreased cell size and increased apoptotic
bodies (cellular suicide). (Neuman
M et al, Alcohol, 26(3), 2002)
Psoriasis and eczema are associated with excessive
alcohol exposure (Higgins E, du
Vivier A, Alcohol and the Skin, Alcohol Alcohol, 27(6), 1992).
Canadian collaborators of mine investigated whether alcohol plays
a role in the pathogenesis of psoriasis by up-regulating humoral
pro-inflammatory cytokines and concluded that in normal
human skin cells, toxicity and psoriasis-causing inflammatory responses
are enhanced by a concentration as low as 40 mM alcohol
(Shear N, Skin Pharmacol Skin Physiol,
12(1-2), 1999). Furthermore, paradoxically, alcohol
concentrations below levels that induce cytotoxicity (0.1–0.5%),
may be immuno-suppressive by inhibiting the inflammatory
response and thereby impairing associated cellular immune responses
to infectious challenge, thereby increasing the risk of
infection for several hours (Saeed
L et al, J Immunol, 173(10), 2004).
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That alcohol exposure is toxic
to human skin cells, is clearly established. The skin, like the liver,
is furthermore one of the few organs capable of metabolising alcohol
to another cytotoxic chemical, acetaldehyde. Glutathione
was greatly reduced in cells consecutively exposed to the alcohol
(a mere one day after another, compared to perpetually, as occurs
in real life use of skin care products). Glutathione is important
for protection from oxidative damage. Lower levels increase vulnerability
of skin cells to oxidative stress by free radicals and other damaging
reactive oxygen species. Conclusion: Alcohol is toxic to human skin
cells. Repeated exposure from skin products may threaten cell viability.
The cytotoxic risks associated with prolonged exposure to alcohol
deserve investigation. Alcohol-free personal care products may prove
less harmful to the skin. (Neuman M
et al, Alcohol, 26(3), 2002) There are several mechanisms
by which alcohol is cytotoxic. Some involve direct cytotoxic action
of alcohol itself, without being metabolised, primarily via the
generation of oxygen radical intermediates and free radicals (Mufti
S et al, Alcohol Alcohol, 28(6), 1993); (Kosaka T et al, Acta Medica
Okayama, 50(3), 1996). The most toxic action
of alcohol results from its even more toxic metabolite, acetaldehyde
(approximately 30 times more toxic), which is produced
from alcohol by several enzymes in human skin (Milton
K, Integrat Comparat Biol, 44(4), 2004). Somewhat reduced
toxicity might result from further breakdown of acetaldehyde (which
is related to formaldehyde) to acidic toxic oxidation transition
products, including carboxylic acids. If acetaldehyde is not eventually
efficiently converted into acetic acid (the acid
in vinegar), severe toxicity can result. (Cheung
C et al, Toxicol, 184(2-3), 2003)
Researchers have detected important classes of enzymes involved
in the biotransformation of both alcohols and aldehydes in human
skin (Cheung C et al, Biochem Biophysic
Res Comm, 261(1), 1999), that present skin sensitisation
hazards with potency relative to the extent of metabolism in the
skin. Alcohol dehydrogenase (ADH) enzymes catalyse the interconversion
of alcohols and aldehydes and convert aldehydes to acids. Aldehyde
dehydrogenase (ALDH) enzymes/catalyse the oxidation of aldehydes
to carboxylic acids. The enzymes are present in human skin, predominantly
in the epidermis and appendages (sebaceous glands and hair follicles).
These enzymes in human skin have toxicological significance i.r.o.
the metabolism of xenobiotic (topically applied solvent tincture
and preservative) ethyl alcohol and the resultant aldehydes. (Cheung
C et al, Toxicol, 184(2-3), 2003)
The enzymatic breakdown of alcohol results in the generation
of the toxic reactive molecule, acetaldehyde and as a byproduct,
highly reactive oxygen radicals that interact with lipid molecules
in cell membranes and via lipid peroxidation, generate additional
reactive molecules, especially malondialdehyde and 4–hydroxy–2–nonenal.
These interact with proteins, lipids and DNA to form adducts (hybrids)
that impede the normal functions of proteins and induce harmful
immune responses. These effects can lead to cellular dysfunction,
cell damage and cell death. (Tuma
D et al, Dangerous By-products of Alcohol Breakdown – Focus
on Adducts, NIAAA, NIH-USA, Oct 2004)
Collagen, the major protein in connective tissue (including
the skin and loss of which results directly in wrinkles), is one
protein preferentially damaged by alcohol aldehydes. Cross-linking
is a process by which “molecular bridges” are formed
between “reactive sites” on different molecules. Acetaldehyde
induced cross-links tie up affected molecules and interfere with
their normal vital functions, which may even be completely blocked.
This process of cross-linking is largely responsible for the visible
age-related changes in human skin that make it inflexible, sagging,
wrinkled and dry. (Fowkes S, Smart
Drug News, 5(5), 1996); (Tuma D et al, NIAAA, 2004)
Alcohol exposure is highly conducive to the generation of oxygen
free radicals and the subsequent attack of fragile polyunsaturated
lipids, thereby producing cytotoxic lipid peroxidation products.
Aberrations in phospholipid and fatty acid metabolism, changes in
cellular redox state, disruptions of the energy state, and increased
production of reactive oxygen metabolites are implicated
in cellular damage resulting from both acute (occasional) and chronic
(ongoing) exposure to alcohol. Non-oxidative metabolism
of alcohol is furthermore an additional toxic mechanism
by which alcohol affects membrane structure and compromises cell
function. (Baker R, Kramer R, Ann
Rev Pharmacol Toxicol, 39(1), 1999); (Corey S et al, In Vitro Cellular
& Develop Biol – Anim, 40(3), 2004)
Alcohol exposure can be directly involved in the production of
reactive oxygen species (ROS) and reactive nitrogen species (RNS),
which form an environment favourable to oxidative stress. ROS and
RNS play an important role in alcohol cytotoxicity
via DNA damage, lipid peroxidation and protein modification. Alcohol-induced
oxidative stress is linked to the metabolism of ethanol involving
both microsomal and mitochondrial systems. Alcohol exposure results
in the depletion of GSH levels and decreases antioxidant activity.
It elevates malondialdehyde, hydroxyethyl radical and hydroxynonenal
protein adducts. These cause the modification of
all biological structures and consequently result in serious malfunction
of cells and tissues. (Das S, Vasudevan
D, Life Sci, 81(3), 2007)
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It is difficult to differentiate
between the tumour-promoting and cancer-causing effects of alcohol
and acetaldehyde, the biological breakdown product of alcohol. They
share similar mechanisms, but the latter is 30 times more toxic.
Alcohol can generate oxygen radical intermediates and free radicals,
leading to lipid peroxidation, which promotes tumours
(Mufti S et al, Alcohol Alcohol,
28(6), 1993). Observations from experimental carcinogenesis
and clinical studies indicate that though it cannot initiate carcinogenesis
by itself, alcohol acts as a tumour promoter. Alcohol
is cytotoxic and the injury induced may cause cell
atrophy or cell death and sometimes, subsequent cell proliferation,
culminating in some facet of neoplastic development. Studies suggest
that long-term alcohol exposure favours malignant development of
chemically induced lesions. Thus, alcohol has can play an active
role where carcinogenesis stimulus are further developed by a dysplastic
proliferative response and possibly an increase in malignancy. (Ronald
Watson, Alcohol and Cancer, CRC Press, 1992); (Cederbaum A, BioFactors,
8(1-2), 1998)
Ethyl alcohol is a very potent radiomimetic agent, producing chromosome
aberrations comparable to those induced by ionizing radiation. A
concentration of 0.12 per cent alcohol produces a small increase
over controls, and 0.25 per cent induces a substantial increase.
A concentration of only 0.5 per cent alcohol was equivalent to about
20 rad/day of chronic gamma radiation, or an accumulated dose of
75 rad. To put this in perspective, the Atomic Energy Commission
maximum permissible dose for radiation workers is a mere 0.1 rad
per week, and for the general public, a miniscule 0.01 rad per week.
(Sax K, Sax H, Proc Nat Acad Sci
USA, 55(6), 1966) Serious shit! DNA reactions with alcohol
occur under physiological conditions in the presence of activating
agents such as free radicals and exposure to UV or visible light.
(Fraenkel-Conrat H, Singer B, Proc Natl Acad Sci USA, 85:3758, 1988)
The European Chemicals Bureau has proposed the classification
of alcohol as a mutagen (ECBI/74/95-Add 3) under the Dangerous
Substances Directive (67/548/EEC) and the German Commission for
the Investigation of Health Hazards of Chemical Compounds classified
it as a Category 2 Mutagen. The genetic effects are mostly due to
the metabolite acetaldehyde, produced in the liver and skin. (Phillips
B, Jenkinson P, Mutagenesis, 16(2), 2001) Alcohol has
been demonstrated to be carcinogenic for various organs and tissues
and must be considered a multipotential carcinogenic agent (Soffritti
M, et al, Annal N Y Acad Sci, 982(1), 2002).
Alcohol itself is not a carcinogen but under certain conditions
is a co-carcinogen and/or tumour promoter. Alcohol exposure
inhibits natural killer (NK) cell activity and reduces NK cell number.
A major impact of alcohol on the immune system favouring tumour
development is undisputed. (Pöschl
G, Seitz H, Alcohol Alcohol, 39(3), 2004) Alcohol
may also stimulate carcinogenesis by inhibiting DNA methylation
(Seitz H, Stickel F, Nat Rev Cancer,
7(8), 2007). Experimental alcohol exposure results in
increases in VEGF mRNA and its receptor protein levels in mammalian
melanoma, with significantly increased melanoma growth
(triple tumour weight) (Tan W et
al, Cancer Biol Ther, 6(8), 2007).
Acetaldehyde is
produced by the oxidation of ethyl alcohol in the body, including
in the skin of humans. Mere micromolar concentrations
of acetaldehyde, causes a wide range of cytopathic
effects associated with multistep carcinogenesis. Acetaldehyde cytotoxicity
causes comparatively higher genotoxicity and inhibits DNA repair
more readily than other major aldehydes in tobacco smoke, automotive
emissions and the manufacturing of plastics. (Grafström
R et al, Carcinogenesis, 15(5), 1994) According to the
International Agency for Research on Cancer there is sufficient
evidence for acetaldehyde as a carcinogen in experimental
animals (Acetaldehyde. Monograph:
Evaluating the Carcinogenic Risk of Chemicals to Humans, Vol. 36,
IARC, Lyons, France, 1995).
Acetaldehyde is genotoxic, inducing gene mutations, clastogenic
effects, and sister-chromatid exchanges in mammalian cells
in the absence of exogenous metabolic activation. There is indirect
evidence from in vitro and in vivo studies to suggest that it can
induce protein-DNA and DNA-DNA cross-links (Rieger
R, Michaelis A, Biol Zent, 679: 1, 1960); (Cortes F et al, Mutat
Res, 171(2-3), 1986); (de Fouw J, Acetaldehyde, Environmental Health
Criteria 167, International Programme on Chemical Safety, UNEP /
ILO / WHO, 1995)
Alcohol and acetaldehyde have both been implicated in carcinogenic
and other cytopathologic processes. These reactions are of biological
concern because they can occur in dilute aqueous solution under
physiological conditions (such as alcohol preservation
of skin / body care products). (Fraenkel-Conrat
H, Singer B, Proc Natl Acad Sci USA, 85:3758, 1988)
Acetaldehyde reacts with and causes DNA damage. Since it is reactive
with the amino residue, it can also react with proteins, amino acids
and RNA molecules. Acetaldehyde causes cancers in animals and tumours,
if not cancer, in humans. (Matsuda
T et al, Nucleic Acid Res, 26(7), 1998)
The metabolism of alcohol leads to the generation of acetaldehyde
and free radicals. Acetaldehyde is carcinogenic and mutagenic, binds
to DNA and proteins, results in hyper-proliferation and is predominantly
responsible for alcohol-associated carcinogenesis. It causes mutations
and gross chromosomal aberrations and interferes with the DNA repair
machinery. Acetaldehyde also binds rapidly to cellular proteins
and DNA, resulting in morphological and functional cellular impairment.
Binding to DNA triggers replication errors and/or mutations. These
acetaldehyde-associated effects occur at concentrations as low as
40 µmol/l, which are similar to concentrations observed in
human saliva following alcohol ingestion (and topical exposure).
(Pöschl G, Seitz H, Alcohol
Alcohol, 39(3), 2004).
Acetaldehyde is however even more toxic than alcohol, but may,
under favourable circumstances, be more safely oxidized to acetate
by aldehyde dehydrogenase. However, alcohol exposure carcinogenesis
involves these same enzymes, the acetaldehyde formed in the first
step being the major culprit, constituting a reactive compound that
forms covalent complexes with proteins and DNA and thus may act
as a mutagen. Alcohol can also induce the cytochrome P450
enzyme that work with alcohol dehydrogenase to oxidize alcohol.
This enzyme also forms dangerous reactive oxygen species that can
activate environmental pro-carcinogens into carcinogenic forms.
(Goodsell D, The Oncologist, 11(9),
2006) Acetaldehyde is one of 13 carcinogens accounting
for approximately 23% of the carcinogenic effects of tobacco smoking
(Sanner T, Dybing E, ‘Carcinogens
in Tobacco Smoke and Quantitative Risk’, The Toxicologist,
96(1), 2007).
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